Inhibition of inducible prostaglandin E(2) synthase by 15-deoxy-Delta(12,14)-prostaglandin J(2) and polyunsaturated fatty acids

Molecular Pathways Governing the Termination of Liver Regeneration

The liver has the unique capacity to regenerate, and up to 70% of the liver can be removed without detrimental consequences to the organism. Liver regeneration is a complex process involving multiple signaling networks and organs. Liver regeneration proceeds through three phases: the initiation phase, the growth phase, and the termination phase. Termination of liver regeneration occurs when the liver reaches a liver-to-body weight that is required for homeostasis, the so-called "hepatostat." The initiation and growth phases have been the subject of many studies. The molecular pathways that govern the termination phase, however, remain to be fully elucidated. This review summarizes the pathways and molecules that signal the cessation of liver regrowth after partial hepatectomy and answers the question, "What factors drive the hepatostat?" SIGNIFICANCE STATEMENT: Unraveling the pathways underlying the cessation of liver regeneration enables the identification of druggable targets that will allow us to gain pharmacological control over liver regeneration. For these purposes, it would be useful to understand why the regenerative capacity of the liver is hampered under certain pathological circumstances so as to artificially modulate the regenerative processes (e.g., by blocking the cessation pathways) to improve clinical outcomes and safeguard the patient's life.

Mechanism of action and potential applications of selective inhibition of microsomal prostaglandin E synthase-1-mediated PGE2 biosynthesis by sonlicromanol's metabolite KH176m

Increased prostaglandin E2 (PGE₂) levels were detected in mitochondrial disease patient cells harboring nuclear gene mutations in structural subunits of complex I, using a metabolomics screening approach. The increased levels of this principal inflammation mediator normalized following exposure of KH176m, an active redox-modulator metabolite of sonlicromanol (KH176). We next demonstrated that KH176m selectively inhibited lipopolysaccharide (LPS) or interleukin-1β (IL-1β)-induced PGE₂ production in control skin fibroblasts. Comparable results were obtained in the mouse macrophage-like cell line RAW264.7. KH176m selectively inhibited mPGES-1 activity, as well as the inflammation-induced expression of mPGES-1. Finally, we showed that the effect of KH176m on mPGES-1 expression is due to the inhibition of a PGE₂-driven positive feedback control-loop of mPGES-1 transcriptional regulation. Based on the results obtained we discuss potential new therapeutic applications of KH176m and its clinical stage parent drug candidate sonlicromanol in mitochondrial disease and beyond.

Inflammation and JNK's Role in Niacin-GPR109A Diminished Flushed Effect in Microglial and Neuronal Cells With Relevance to Schizophrenia

Schizophrenia is a neuropsychiatric illness with no single definitive aetiology, making its treatment difficult. Antipsychotics are not fully effective because they treat psychosis rather than the cognitive or negative symptoms. Antipsychotics fail to alleviate symptoms when patients enter the chronic stage of illness. Topical application of niacin showed diminished skin flush in the majority of patients with schizophrenia compared to the general population who showed flushing. The niacin skin flush test is useful for identifying patients with schizophrenia at their ultra-high-risk stage, and understanding this pathology may introduce an effective treatment. This review aims to understand the pathology behind the diminished skin flush response, while linking it back to neurons and microglia. First, it suggests that there are altered proteins in the GPR109A-COX-prostaglandin pathway, inflammatory imbalance, and kinase signalling pathway, c-Jun N-terminal kinase (JNK), which are associated with diminished flush. Second, genes from the GPR109A-COX-prostaglandin pathway were matched against the 128-loci genome wide association study (GWAS) for schizophrenia using GeneCards, suggesting that G-coupled receptor-109A (GPR109A) may have a genetic mutation, resulting in diminished flush. This review also suggests that there may be increased pro-inflammatory mediators in the GPR109A-COX-prostaglandin pathway, which contributes to the diminished flush pathology. Increased levels of pro-inflammatory markers may induce microglial-activated neuronal death. Lastly, this review explores the role of JNK on pro-inflammatory mediators, proteins in the GPR109A-COX-prostaglandin pathway, microglial activation, and neuronal death. Inhibiting JNK may reverse the changes observed in the diminished flush response, which might make it a good therapeutic target.

Metabolomic analysis of low and high biofilm-forming Helicobacter pylori strains

The biofilm-forming-capability of Helicobacter pylori has been suggested to be among factors influencing treatment outcome. However, H. pylori exhibit strain-to-strain differences in biofilm-forming-capability. Metabolomics enables the inference of spatial and temporal changes of metabolic activities during biofilm formation. Our study seeks to examine the differences in metabolome of low and high biofilm-formers using the metabolomic approach. Eight H. pylori clinical strains with different biofilm-forming-capability were chosen for metabolomic analysis. Bacterial metabolites were extracted using Bligh and Dyer method and analyzed by Liquid Chromatography/Quadrupole Time-of-Flight mass spectrometry. The data was processed and analyzed using the MassHunter Qualitative Analysis and the Mass Profiler Professional programs. Based on global metabolomic profiles, low and high biofilm-formers presented as two distinctly different groups. Interestingly, low-biofilm-formers produced more metabolites than high-biofilm-formers. Further analysis was performed to identify metabolites that differed significantly (p-value < 0.005) between low and high biofilm-formers. These metabolites include major categories of lipids and metabolites involve in prostaglandin and folate metabolism. Our findings suggest that biofilm formation in H. pylori is complex and probably driven by the bacterium’ endogenous metabolism. Understanding the underlying metabolic differences between low and high biofilm-formers may enhance our current understanding of pathogenesis, extragastric survival and transmission of H. pylori infections.

Microsomal Prostaglandin E Synthase-1 Expression by Aortic Smooth Muscle Cells Attenuates the Differentiated Phenotype

The development of numerous types of cardiovascular disease is associated with alteration of the vascular smooth muscle cell (SMC) phenotype. We have previously shown that abdominal aortic aneurysm progression in a mouse model of the disease is associated with reduced differentiation of SMCs within the lesion and that cyclooxygenase-2 (COX-2) is critical to initiation and progression of the aneurysms. The current studies used human aortic SMC (hASMC) cultures to better characterize mechanisms responsible for COX-2-dependent modulation of the SMC phenotype. Depending on the culture conditions, hASMCs expressed multiple characteristics of a differentiated and contractile phenotype, or a dedifferentiated and secretory phenotype. The pharmacological inhibition of COX-2 promoted the differentiated phenotype, whereas treatment with the COX-2-derived metabolite prostaglandin E2 (PGE2) increased characteristics of the dedifferentiated phenotype. Furthermore, pharmacological inhibition or siRNA-mediated knockdown of microsomal prostaglandin E synthase-1 (mPGES-1), the enzyme that functions downstream of COX-2 during the synthesis of PGE2, significantly increased expression of characteristics of the differentiated SMC phenotype. Therefore, our findings suggest that COX-2 and mPGES-1-dependent synthesis of PGE2 contributes to a dedifferentiated hASMC phenotype and that mPGES-1 may provide a novel pharmacological target for treatment of cardiovascular diseases where altered SMC differentiation has a causative role.

Computational models for the classification of mPGES-1 inhibitors with fingerprint descriptors

Human microsomal prostaglandin [Formula: see text] synthase (mPGES)-1 is a promising drug target for inflammation and other diseases with inflammatory symptoms. In this work, we built classification models which were able to classify mPGES-1 inhibitors into two groups: highly active inhibitors and weakly active inhibitors. A dataset of 1910 mPGES-1 inhibitors was separated into a training set and a test set by two methods, by a Kohonen's self-organizing map or by random selection. The molecules were represented by different types of fingerprint descriptors including MACCS keys (MACCS), CDK fingerprints, Estate fingerprints, PubChem fingerprints, substructure fingerprints and 2D atom pairs fingerprint. First, we used a support vector machine (SVM) to build twelve models with six types of fingerprints and found that MACCS had some advantage over the other fingerprints in modeling. Next, we used naïve Bayes (NB), random forest (RF) and multilayer perceptron (MLP) methods to build six models with MACCS only and found that models using RF and MLP methods were better than NB. Finally, all the models with MACCS keys were used to make predictions on an external test set of 41 compounds. In summary, the models built with MACCS keys and using SVM, RF and MLP methods show good prediction performance on the test sets and the external test set. Furthermore, we made a structure-activity relationship analysis between mPGES-1 and its inhibitors based on the information gain of fingerprints and could pinpoint some key functional groups for mPGES-1 activity. It was found that highly active inhibitors usually contained an amide group, an aromatic ring or a nitrogen heterocyclic ring, and several heteroatoms substituents such as fluorine and chlorine. The carboxyl group and sulfur atom groups mainly appeared in weakly active inhibitors.

Nonsteroidal Anti-Inflammatory Therapy: A Journey Toward Safety

The efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) against inflammation, pain, and fever has been supporting their worldwide use in the treatment of painful conditions and chronic inflammatory diseases until today. However, the long-term therapy with NSAIDs was soon associated with high incidences of adverse events in the gastrointestinal tract. Therefore, the search for novel drugs with improved safety has begun with COX-2 selective inhibitors (coxibs) being straightaway developed and commercialized. Nevertheless, the excitement has fast turned to disappointment when diverse coxibs were withdrawn from the market due to cardiovascular toxicity. Such events have once again triggered the emergence of different strategies to overcome NSAIDs toxicity. Here, an integrative review is provided to address the breakthroughs of two main approaches: (i) the association of NSAIDs with protective mediators and (ii) the design of novel compounds to target downstream and/or multiple enzymes of the arachidonic acid cascade. To date, just one phosphatidylcholine-associated NSAID has already been approved for commercialization. Nevertheless, the preclinical and clinical data obtained so far indicate that both strategies may improve the safety of nonsteroidal anti-inflammatory therapy.

Chemistry and biology of microsomal prostaglandin E2 synthase-1 (mPGES-1) inhibitors as novel anti-inflammatory agents: recent developments and current status

Prostaglandin (PG) E₂, a key mediator of inflammatory pain and fever, is biosynthesized from PGH₂ by mPGES-1.

Targeting inflammation: multiple innovative ways to reduce prostaglandin E₂

The PGE2 pathway is important in inflammation-driven diseases and specific targeting of the inducible mPGES-1 is warranted due to the cardiovascular problems associated with the long-term use of COX-2 inhibitors. This review focuses on patents issued on methods of measuring mPGES-1 activity, on drugs targeting mPGES-1 and on other modulators of free extracellular PGE2 concentration. Perspectives and conclusions regarding the status of these drugs are also presented. Importantly, no selective inhibitors targeting mPGES-1 have been identified and, despite the high number of published patents, none of these drugs have yet made it to clinical trials.

Role of mitochondria in programmed cell death mediated by arachidonic acid-derived eicosanoids

Arachidonic acid-derived eicosanoids from cyclooxygenases, lipoxygenases, and cytochrome P450 are important lipid mediators involved in numerous homeostatic and pathophysiological processes. Most eicosanoids act primarily on their respective cell surface G-protein coupled receptors to elicit downstream signaling in an autocrine and paracrine fashion. Emerging evidence indicates that these hormones are also critical in apoptosis in a cell/tissue specific manner. In this review, we summarize the formation of eicosanoids and their roles as mediators in apoptosis, specifically on the roles of mitochondria in mediating these events and the signaling pathways involved. The biological relevance of eicosanoid-mediated apoptosis is also discussed.

Microsomal Prostaglandin E2 Synthase-1

The prostanoids and leukotrienes (LTs) formed from arachidonic acid (AA) via the cyclooxygenase (COX)-1/2 and 5-lipoxygenase (5-LO) pathway, respectively, mediate inflammatory responses, chronic tissue remodelling, cancer, asthma and autoimmune disorders, but also possess homeostatic functions in the gastrointestinal tract, uterus, brain, kidney, vasculature and host defence. Based on the manifold functions of these eicosanoids, the clinical use of non-steroidal anti-inflammatory drugs (NSAIDs), a class of drugs that block formation of all prostanoids, is hampered by severe side-effects including gastrointestinal injury, renal irritations and cardiovascular risks. Therefore, anti-inflammatory agents interfering with eicosanoid biosynthesis require a well-balanced pharmacological profile to minimize these on-target side-effects. Current anti-inflammatory research aims at identifying compounds that can suppress the massive formation of pro-inflammatory prostaglandin (PG)E2 without affecting homeostatic PGE2 and PGI2 synthesis. The inducible microsomal prostaglandin E2 synthase-1 (mPGES-1) is one promising target enzyme. We will give an overview about the structure, regulation and function of mPGES-1 and then present novel inhibitors of mPGES-1 that may possess a promising pharmacological profile.

Observation of two modes of inhibition of human microsomal prostaglandin E synthase 1 by the cyclopentenone 15-deoxy-Δ(12,14)-prostaglandin J(2)

Microsomal prostaglandin E synthase 1 (MPGES1) is an enzyme that produces the pro-inflammatory molecule prostaglandin E(2) (PGE(2)). Effective inhibitors of MPGES1 are of considerable pharmacological interest for the selective control of pain, fever, and inflammation. The isoprostane, 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ(2)), a naturally occurring degradation product of prostaglandin D(2), is known to have anti-inflammatory properties. In this paper, we demonstrate that 15d-PGJ(2) can inhibit MPGES1 by covalent modification of residue C59 and by noncovalent inhibition through binding at the substrate (PGH(2)) binding site. The mechanism of inhibition is dissected by analysis of the native enzyme and the MPGES1 C59A mutant in the presence of glutathione (GSH) and glutathione sulfonate. The location of inhibitor adduction and noncovalent binding was determined by triple mass spectrometry sequencing and with backbone amide H/D exchange mass spectrometry. The kinetics, regiochemistry, and stereochemistry of the spontaneous reaction of GSH with 15d-PGJ(2) were determined. The question of whether the anti-inflammatory properties of 15d-PGJ(2) are due to inhibition of MPGES1 is discussed.

Identification and development of mPGES-1 inhibitors: where we are at?

Microsomal prostaglandin E synthase-1 (mPGES-1) is the terminal synthase responsible for the synthesis of the pro-tumorigenic prostaglandin E(2) (PGE(2)). mPGES-1 is overexpressed in a wide variety of cancers. Since its discovery in 1997 by Bengt Samuelsson and collaborators, the enzyme has been the object of over 200 peer-reviewed articles. Although today mPGES-1 is considered a validated and promising therapeutic target for anticancer drug discovery, challenges in inhibitor design and selectivity are such that up to this date there are only a few published records of small-molecule inhibitors targeting the enzyme and exhibiting some in vivo anticancer activity. This review summarizes the structures, and the in vitro and in vivo activities of these novel mPGES-1 inhibitors. Challenges that have been encountered are also discussed.

Novel human mPGES-1 inhibitors identified through structure-based virtual screening

Microsomal prostaglandin E synthase-1 (mPGES-1) is an inducible prostaglandin E synthase after exposure to pro-inflammatory stimuli and, therefore, represents a novel target for therapeutic treatment of acute and chronic inflammatory disorders. It is essential to identify mPGES-1 inhibitors with novel scaffolds as new leads or hits for the purpose of drug design and discovery that aim to develop the next-generation anti-inflammatory drugs. Herein we report novel mPGES-1 inhibitors identified through a combination of large-scale structure-based virtual screening, flexible docking, molecular dynamics simulations, binding free energy calculations, and in vitro assays on the actual inhibitory activity of the computationally selected compounds. The computational studies are based on our recently developed three-dimensional (3D) structural model of mPGES-1 in its open state. The combined computational and experimental studies have led to identification of new mPGES-1 inhibitors with new scaffolds. In particular, (Z)-5-benzylidene-2-iminothiazolidin-4-one is a promising novel scaffold for the further rational design and discovery of new mPGES-1 inhibitors. To our best knowledge, this is the first time a 3D structural model of the open state mPGES-1 is used in structure-based virtual screening of a large library of available compounds for the mPGES-1 inhibitor identification. The positive experimental results suggest that our recently modeled trimeric structure of mPGES-1 in its open state is ready for the structure-based drug design and discovery.

Peroxisome proliferator-activated receptors and progression of colorectal cancer

The peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. These receptors are also ligand-dependent transcription factors responsible for the regulation of cellular events that range from glucose and lipid homeostases to cell differentiation and apoptosis. The importance of these receptors in lipid homeostasis and energy balance is well established. In addition to these metabolic and anti-inflammatory properties, emerging evidence indicates that PPARs can function as either tumor suppressors or accelerators, suggesting that these receptors are potential candidates as drug targets for cancer prevention and treatment. However, conflicting results have emerged regarding the role of PPARs on colon carcinogenesis. Therefore, further investigation is warranted prior to considering modulation of PPARs as an efficacious therapy for colorectal cancer chemoprevention and treatment.

Pharmacophore modeling and virtual screening for novel acidic inhibitors of microsomal prostaglandin E₂ synthase-1 (mPGES-1)

Microsomal prostaglandin E₂ synthase-1 (mPGES-1) catalyzes prostaglandin E₂ formation and is considered as a potential anti-inflammatory pharmacological target. To identify novel chemical scaffolds active on this enzyme, two pharmacophore models for acidic mPGES-1 inhibitors were developed and theoretically validated using information on mPGES-1 inhibitors from literature. The models were used to screen chemical databases supplied from the National Cancer Institute (NCI) and the Specs. Out of 29 compounds selected for biological evaluation, nine chemically diverse compounds caused concentration-dependent inhibition of mPGES-1 activity in a cell-free assay with IC₅₀ values between 0.4 and 7.9 μM, respectively. Further pharmacological characterization revealed that also 5-lipoxygenase (5-LO) was inhibited by most of these active compounds in cell-free and cell-based assays with IC₅₀ values in the low micromolar range. Together, nine novel chemical scaffolds inhibiting mPGES-1 are presented that may possess anti-inflammatory properties based on the interference with eicosanoid biosynthesis.

Lipid metabolism and peroxisome proliferator-activated receptor signaling pathways participate in late-phase liver regeneration

Liver regeneration (LR) is of great clinical significance in various liver-associated diseases. LR proceeds along a sequence of three distinct phases: priming/initiation, proliferation, and termination. Compared with the recognition of the first two phases, little is known about LR termination and structure/function reorganization. A combination of "omics" techniques, along with bioinformatics, may provide new insights into the molecular mechanism of the late-phase LR. Gene, protein, and metabolite profiles of the rat liver were determined by cDNA microarray, two-dimensional electrophoresis, and HPLC-MS analysis. Pathway enrichment analysis was performed to identify the pathways: 427 differentially expressed genes extracted from the microarray experiment revealed two expression patterns representing the early and late phase of LR. Functionally, the genes expressing at a higher level at the early phase than at the late phase were mainly involved in the response to stress, proliferation, and resistance to apoptosis, while those expressing at a lower level at the early phase than at the late phase were mainly engaged in lipid metabolism. Compared with the sham-operation control (SH) group, 5 proteins in the 70% partial hepatectomy (70%PHx) group were upregulated at the protein level, and 3 proteins were downregulated at 168 h after the 70%PHx. E-FABP, an upregulated fatty acid binding protein, was found to be involved in the peroxisome proliferator-activated receptor (PPAR) signaling pathway. The metabolomic data confirmed the enhancement of lipid metabolism by the detection of the intermediate and final metabolites. We've concluded that increased lipid metabolism and activated PPAR signaling pathways play important roles in late-phase LR.

mPGES-1 as a target for cancer suppression: A comprehensive invited review "Phospholipase A2 and lipid mediators"

Prostaglandin E(2) (PGE(2)) is a bioactive lipid that can elicit a wide range of biological effects associated with inflammation and cancer. The physiological roles of PGE(2) are diverse, mediated in part through activation of key downstream signaling cascades via transmembrane EP receptors located on the cell surface. Elevated levels of COX-2 and concomitant overproduction of PGE(2) are often found in human cancers. These observations have led to the use of non-steroidal anti-inflammatory drugs (NSAIDs) as chemopreventive agents, particularly for colorectal cancer (CRC). Their long-term use, however, may be associated with gastrointestinal toxicity and increased risk of adverse cardiovascular events, prompting the development of other enzymatic targets in this pathway. This review will focus on recent efforts to target the terminal synthase, mPGES-1, for cancer chemoprevention. The role of mPGES-1 in the pathogenesis of various cancers is discussed. In addition, an overview of recent efforts to develop small molecule inhibitors that target the protein with high selectivity is also be reviewed.

Myrtucommulone, a natural acylphloroglucinol, inhibits microsomal prostaglandin E(2) synthase-1

BACKGROUND AND PURPOSE

The selective inhibition of prostaglandin (PG)E(2) formation via interference with microsomal PGE(2) synthase (mPGES)-1 could have advantages in the treatment of PGE(2)-associated diseases, such as inflammation, fever and pain, compared with a general suppression of all PG biosynthesis, provided by inhibition of cyclooxygenase (COX)-1 and 2. Here, we addressed whether the naturally occurring acylphloroglucinol myrtucommulone (MC) from Myrtus communis L. (myrtle) affected mPGES-1.

EXPERIMENTAL APPROACH

The effect of MC on PGE(2) formation was investigated in a cell-free assay by using microsomal preparations of interleukin-1beta-stimulated A549 cells as the source of mPGES-1, in intact A549 cells, and in lipopolysaccharide-stimulated human whole blood. Inhibition of COX-1 and COX-2 activity in cellular and cell-free assays was assessed by measuring 12(S)-hydroxy-5-cis-8,10-trans-heptadecatrienoic acid and 6-oxo PGF(1alpha) formation.

KEY RESULTS

MC concentration-dependently inhibited cell-free mPGES-1-mediated conversion of PGH(2) to PGE(2) (IC(50) = 1 micromol x L(-1)). PGE(2) formation was also diminished in intact A549 cells as well as in human whole blood at low micromolar concentrations. Neither COX-2 activity in A549 cells nor isolated human recombinant COX-2 was significantly affected by MC up to 30 micromol x L(-1), and only moderate inhibition of cellular or cell-free COX-1 was evident (IC(50) > 15 micromol x L(-1)).

CONCLUSIONS AND IMPLICATIONS

MC is the first natural product to inhibit mPGES-1 that efficiently suppresses PGE(2) formation without significant inhibition of the COX enzymes. This provides an interesting pharmacological profile suitable for interventions in inflammatory disorders, without the typical side effects of coxibs and non-steroidal anti-inflammatory drugs.

Inhibition of cyclooxygenases 1 and 2 by the phospholipase-blocker, arachidonyl trifluoromethyl ketone

BACKGROUND AND PURPOSE

Arachidonyl trifluoromethyl ketone (ATK) is widely used as an inhibitor of cytosolic group IV phospholipase A(2) (cPLA(2)) and calcium-independent group VI phospholipase A(2) (iPLA(2)). ATK thus reduces arachidonic acid (AA) substrate for cyclooxygenase (COX; also known as prostaglandin H synthase) and attenuates prostaglandin (PG) synthesis. It has been shown previously, that ATK blocks thromboxane B(2) production induced by exogenous AA in human platelets. It remains, however, unknown whether ATK also directly modulates the activity of cyclooxygenase (COX).

EXPERIMENTAL APPROACH

Time courses for inhibition of COX by ATK was obtained using osteoblast-like MC3T3-E1 cells, with exogenous AA as substrate and the pure enzymes COX-1 and COX-2. PGE(2) was measured by GC-MS.

KEY RESULTS

ATK was a potent inhibitor of COX-1 and COX-2 with IC(50) values of 0.5 and 0.1 microM in MC3T3-E1 cells and of 1.7 and 2.6 microM using the pure enzymes. Inhibition was reversible, with slow- and tight-binding characteristics. The arachidonyl carbon chain was essential, as the saturated palmitoyl analogue had no effect.

CONCLUSIONS AND IMPLICATIONS

Attenuation of PG synthesis by ATK is taken to be the consequence of PLA(2) inhibition and the findings of many studies are interpreted on that basis. If there are, however, alternative routes for AA liberation (such as phospholipase C/diacyl glycerol lipase or phospholipase D), this interpretation can lead to false conclusions. As ATK is a widely used and important pharmacological tool in eicosanoid research, knowledge of its interactions with other major enzymes of the cascade is of considerable importance.

Role of peroxisome proliferator-activated receptor-gamma (PPARgamma) during liver regeneration in rats

BACKGROUND AND AIM

Peroxisome proliferator-activated receptor-gamma (PPARgamma), a member of the nuclear receptor superfamily, is widely expressed in adipocytes and other tissues, including the liver. Several reports have shown that PPARgamma activation induced cell-cycle arrest and apoptosis in tumor cells. We investigated the role of the PPARgamma/ligand system and the effect of the PPARgamma agonist during liver regeneration.

METHODS

Expression of PPARgamma and serum levels of 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) by enzyme immunoassay were evaluated in rats following partial hepatectomy (PH group). Further, the effect of the PPARgamma agonist, pioglitazone, on liver regeneration (PH + PGZ group) was evaluated by proliferating cell nuclear antigen labeling index, relative liver weight, and expression of cell-cycle regulators.

RESULTS

The number of PPARgamma-stained hepatocytes decreased at 24 h (PH, 15.8 +/- 2.2%; sham, 35.5 +/- 2.4%; P < 0.001) and increased in the late phase of liver regeneration compared to the sham-operated group (P < 0.001 at 48-120 h). The peaks of serum 15d-PGJ2 (627.0 +/- 91.1 pg/ml) and PPARgamma expression (90.6 +/- 3.1%) coincided in the late phase of liver regeneration. Also, oral administration of pioglitazone inhibited hepatocyte proliferation, in terms of the proliferating cell nuclear antigen (PCNA) labeling index and p27 expression during the late phase of liver regeneration, and caused a transient reduction in liver mass when compared to the PH group.

CONCLUSIONS

These results indicate that the PPARgamma/ligand system may be one of the key negative regulators of hepatocyte proliferation and may be responsible for the inhibition of liver growth in the late phase of liver regeneration.

Photo-crosslinking of proteins in intact cells reveals a dimeric structure of cyclooxygenase-2 and an inhibitor-sensitive oligomeric structure of microsomal prostaglandin E2 synthase-1

We have characterized the structures of cyclooxygenase-2 (COX-2) and microsomal prostaglandin E(2) synthase-1 (mPGES-1) in intact cells using bifunctional and photo-activatable crosslinking agents. A dimeric complex was detected for COX-2 by both crosslinking approaches, consistent with the crystal structure of the enzyme. For mPGES-1, treatment of A549 cells with disuccinimidyl suberate yielded immunoreactive protein bands corresponding to a dimer (33 kDa) and a trimer (45 kDa), as observed for the isolated enzyme. Photo-crosslinking with photoactivatable methionine in intact cells generated complexes with molecular weights corresponding to the dimer (33 kDa) and two putative trimer forms (50 and 55 kDa). Treatment with the selective mPGES-1 inhibitor MF63 prevented the formation of the 50 and 55 kDa crosslinked complexes, while an inactive structural analogue had no effect. Our data indicate that COX-2 forms a dimer in intact cells and that mPGES-1 has an oligomeric structure that can be disrupted by a selective inhibitor.

Membrane prostaglandin E synthase-1: a novel therapeutic target

Prostaglandin E(2) (PGE(2)) is the most abundant prostaglandin in the human body. It has a large number of biological actions that it exerts via four types of receptors, EP1-4. PGE(2) is formed from arachidonic acid by cyclooxygenase (COX-1 and COX-2)-catalyzed formation of prostaglandin H(2) (PGH(2)) and further transformation by PGE synthases. The isomerization of the endoperoxide PGH(2) to PGE(2) is catalyzed by three different PGE synthases, viz. cytosolic PGE synthase (cPGES) and two membrane-bound PGE synthases, mPGES-1 and mPGES-2. Of these isomerases, cPGES and mPGES-2 are constitutive enzymes, whereas mPGES-1 is mainly an induced isomerase. cPGES uses PGH(2) produced by COX-1 whereas mPGES-1 uses COX-2-derived endoperoxide. mPGES-2 can use both sources of PGH(2). mPGES-1 is a member of the membrane associated proteins involved in eicosanoid and glutathione metabolism (MAPEG) superfamily. It requires glutathione as an essential cofactor for its activity. mPGES-1 is up-regulated in response to various proinflammatory stimuli with a concomitant increased expression of COX-2. The coordinate increased expression of COX-2 and mPGES-1 is reversed by glucocorticoids. Differences in the kinetics of the expression of the two enzymes suggest distinct regulatory mechanisms for their expression. Studies, mainly from disruption of the mPGES-1 gene in mice, indicate key roles of mPGES-1-generated PGE(2) in female reproduction and in pathological conditions such as inflammation, pain, fever, anorexia, atherosclerosis, stroke, and tumorigenesis. These findings indicate that mPGES-1 is a potential target for the development of therapeutic agents for treatment of several diseases.

3D-QSAR study of microsomal prostaglandin E2 synthase (mPGES-1) inhibitors

Microsomal prostaglandin E(2) synthase (mPGES-1) has been identified recently as a novel target for treating pain and inflammation. The aim of this study is to understand the binding affinities of reported inhibitors for mPGES-1 and further to design potential new mPGES-1 inhibitors. 3D-QSAR-CoMFA (comparative molecular field analysis) and CoMSIA (comparative molecular similarity indices analysis) - techniques were employed on a series of indole derivatives that act as selective mPGES-1 inhibitors. The lowest energy conformer of the most active compound obtained from systematic conformational search was used as a template for the alignment of 32 compounds. The models obtained were used to predict the activities of the test set of eight compounds, and the predicted values were in good agreement with the experimental results. The 3D-QSAR models derived from the training set of 24 compounds were all statistically significant (CoMFA; q (2) = 0.89, r (2) = 0.95, [Formula: see text], [Formula: see text] and CoMSIA; q (2) = 0.84, r (2) = 0.93, [Formula: see text], [Formula: see text]). Contour plots generated for the CoMFA and CoMSIA models reveal useful clues for improving the activity of mPGES-1 inhibitors. In particular, substitutions of an electronegative fluorine atom or a bulky hydrophilic phenoxy group at the meta or para positions of the biphenyl rings might improve inhibitory activity. A plausible binding mode between the ligands and mPGES-1 is also proposed.

Signal pathways involved in the regulation of prostaglandin E synthase-1 in human gingival fibroblasts

Microsomal prostaglandin E synthase-1 (mPGES-1) is the terminal enzyme regulating the synthesis of prostaglandin E2 (PGE2) in inflammatory conditions. In this study we investigated the regulation of mPGES-1 in gingival fibroblasts stimulated with the inflammatory mediators interleukin-1 beta (IL-1beta) and tumour necrosis factor alpha (TNFalpha). The results showed that IL-1beta and TNFalpha induce the expression of mPGES-1 without inducing the expression of early growth response factor-1 (Egr-1). Treatment of the cells with the PLA2 inhibitor 4-bromophenacyl bromide (BPB) decreased the cytokine-induced mPGES-1 expression accompanied by decreased PGE2 production whereas the addition of arachidonic acid (AA) upregulated mPGES-1 expression and PGE2 production. The protein kinase C (PKC) activator PMA did not upregulate the expression of mPGES-1 in contrast to COX-2 expression and PGE2 production. In addition, inhibitors of PKC, tyrosine and p38 MAP kinase markedly decreased the cytokine-induced PGE2 production but not mPGES-1 expression. Moreover, the prostaglandin metabolites PGE2 and PGF2alpha induced mPGES-1 expression as well as upregulated the cytokine-induced mPGES-1 expression indicating positive feedback regulation of mPGES-1 by prostaglandin metabolites. The peroxisome proliferator-activated receptor-gamma (PPARgamma) ligand, 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), decreased mPGES-1 expression but not COX-2 expression or PGE2 production. The results indicate that the inflammatory-induced mPGES-1 expression is regulated by PLA2 and 15d-PGJ2 but not by PKC, tyrosine kinase or p38 MAP kinase providing new insights into the regulation of mPGES-1.

Endotoxic fever: New concepts of its regulation suggest new approaches to its management

Endotoxic fever is regulated by endogenous factors that provide pro- and anti-pyretic signals at different points along the febrigenic pathway, from the periphery to the brain. Current evidence indicates that the febrile response to invading Gram-negative bacteria and their products is initiated upon their arrival in the liver via the circulation and their uptake by Kupffer cells (Kc). These pathogens activate the complement cascade on contact, hence generating complement component 5a. It, in turn, very rapidly stimulates Kc to release prostaglandin (PG)E2. Pyrogenic cytokines (TNF-alpha, etc.) are produced later and are no longer considered to be the immediate triggers of fever. The Kc-generated PGE2 either (1) may be transported by the bloodstream to the ventromedial preoptic-anterior hypothalamus (POA, the locus of the temperature-regulating center), presumptively diffusing into it and acting on thermoregulatory neurons; PGE2 is thus taken to be the final, central fever mediator. Or (2) it may activate hepatic vagal afferents projecting to the medulla oblongata, thence to the POA via the ventral noradrenergic bundle. Norepinephrine consequently secreted stimulates alpha1-adrenoceptors on thermoregulatory neurons, rapidly evoking an initial rise in core temperature (Tc) not associated with any change in POA PGE2; this neural, PGE2-independent signaling pathway is quicker than the blood-borne route. Elevated POA PGE2 and a secondary Tc rise occur later, consequent to alpha2 stimulation. Endogenous counter-regulatory factors are also elaborated peripherally and centrally at different points during the course of the febrile response; they are, therefore, anti-pyretic. These multiple interacting pathways are the subject of this review.

15-deoxy-Δ12,14-prostaglandin J2 inhibits the expression of microsomal prostaglandin E synthase type 2 in colon cancer cells

Prostaglandin (PG) E(2) (PGE(2)) plays a predominant role in promoting colorectal carcinogenesis. The biosynthesis of PGE(2) is accomplished by conversion of the cyclooxygenase (COX) product PGH(2) by several terminal prostaglandin E synthases (PGES). Among the known PGES isoforms, microsomal PGES type 1 (mPGES-1) and type 2 (mPGES-2) were found to be overexpressed in colorectal cancer (CRC); however, the role and regulation of these enzymes in this malignancy are not yet fully understood. Here, we report that the cyclopentenone prostaglandins (CyPGs) 15-deoxy-Delta(12,14)-PGJ(2) and PGA(2) downregulate mPGES-2 expression in the colorectal carcinoma cell lines Caco-2 and HCT 116 without affecting the expression of any other PGES or COX. Inhibition of mPGES-2 was subsequently followed by decreased microsomal PGES activity. These effects were mediated via modulation of the cellular thiol-disulfide redox status but did not involve activation of the peroxisome proliferator-activated receptor gamma or PGD(2) receptors. CyPGs had antiproliferative properties in vitro; however, this biological activity could not be directly attributed to decreased PGES activity because it could not be reversed by adding PGE(2). Our data suggest that there is a feedback mechanism between PGE(2) and CyPGs that implicates mPGES-2 as a new potential target for pharmacological intervention in CRC.

Contrasting effects of peroxisome-proliferator-activated receptor (PPAR)gamma agonists on membrane-associated prostaglandin E2 synthase-1 in IL-1beta-stimulated rat chondrocytes: evidence for PPARgamma-independent inhibition by 15-deoxy-Delta12,14prostaglandin J2

Microsomal prostaglandin E synthase (mPGES)-1 is a newly identified inducible enzyme of the arachidonic acid cascade with a key function in prostaglandin (PG)E2 synthesis. We investigated the kinetics of inducible cyclo-oxygenase (COX)-2 and mPGES-1 expression with respect to the production of 6-keto-PGF1alpha and PGE2 in rat chondrocytes stimulated with 10 ng/ml IL-1beta, and compared their modulation by peroxisome-proliferator-activated receptor (PPAR)gamma agonists. Real-time PCR analysis showed that IL-1beta induced COX-2 expression maximally (37-fold) at 12 hours and mPGES-1 expression maximally (68-fold) at 24 hours. Levels of 6-keto-PGF1alpha and PGE2 peaked 24 hours after stimulation with IL-1beta; the induction of PGE2 was greater (11-fold versus 70-fold, respectively). The cyclopentenone 15-deoxy-Delta12,14prostaglandin J2 (15d-PGJ2) decreased prostaglandin synthesis in a dose-dependent manner (0.1 to 10 microM), with more potency on PGE2 level than on 6-keto-PGF1alpha level (-90% versus -66% at 10 microM). A high dose of 15d-PGJ2 partly decreased COX-2 expression but decreased mPGES-1 expression almost completely at both the mRNA and protein levels. Rosiglitazone was poorly effective on these parameters even at 10 microM. Inhibitory effects of 10 microM 15d-PGJ2 were neither reduced by PPARgamma blockade with GW-9662 nor enhanced by PPARgamma overexpression, supporting a PPARgamma-independent mechanism. EMSA and TransAM analyses demonstrated that mutated IkappaBalpha almost completely suppressed the stimulating effect of IL-1beta on mPGES-1 expression and PGE2 production, whereas 15d-PGJ2 inhibited NF-kappaB transactivation. These data demonstrate the following in IL-1-stimulated rat chondrocytes: first, mPGES-1 is rate limiting for PGE2 synthesis; second, activation of the prostaglandin cascade requires NF-kappaB activation; third, 15d-PGJ2 strongly inhibits the synthesis of prostaglandins, in contrast with rosiglitazone; fourth, inhibition by 15d-PGJ2 occurs independently of PPARgamma through inhibition of the NF-kappaB pathway; fifth, mPGES-1 is the main target of 15d-PGJ2.

Prostaglandin E synthase in the pathophysiology of arthritis

Prostaglandin E synthase (PGES) is a recently identified terminal enzyme that acts downstream of cyclooxygenase and catalyzes the conversion of prostaglandin (PG) H2 to PGE2. At least three isozymes have been cloned so far, which are called membrane-associated PGES (mPGES)-1, mPGES-2, and cytosolic PGES. Among them, mPGES-1 is induced by various inflammatory stimuli in some cells and tissues. Induction of mPGES-1 in the component of articular tissues of patients with rheumatoid arthritis and osteoarthritis has been demonstrated in vitro. Recent studies using adjuvant induced arthritis model have shown the increase of mPGES-1 expression resulted in the increase of PGE2 production at the sites of inflammation. In addition, reports of mPGES-1-deficient mice clearly suggest the role of mPGES-1 in the process of chronic inflammation such as collagen-induced arthritis and collagen antibody induced arthritis in vivo. Thus, recent in vitro and in vivo findings suggest that mPGES-1 may be a novel therapeutic target for arthritis. This paper introduces recent advances in research about the role of PGES in the pathophysiology of arthritis.

An automated multistep high-throughput screening assay for the identification of lead inhibitors of the inducible enzyme mPGES-1

Prostaglandin E2 synthase (mPGES-1), the enzyme which catalyzes the synthesis of PGE2, is induced during the inflammatory response. For this reason, mPGES-1 could be a potential therapeutic target. A high-throughput screening assay was developed to identify potential inhibitors of mPGES-1. The assay consisted of a 30-s mPGES-1 enzymatic reaction followed by the detection of PGE2 by enzyme immunoassay (EIA). The enzymatic reaction was performed in a batch mode because the instability of the substrate (10 min) limited the number of plates assayed within a working day. The detection of the product by EIA was performed on 3 instruments requiring 14 different steps for complete automation. The authors describe here the optimization and implementation of a 2-part assay on a Thermo CRS robotic system. More than 315,000 compounds were tested, and a hit rate of 0.84% was obtained for this assay. Although the entire assay required multiple steps, the assay was successfully miniaturized and automated for a high-throughput screening campaign.

Inhibitors of the inducible microsomal prostaglandin E2 synthase (mPGES-1) derived from MK-886

A series of potent and selective inhibitors of the inducible microsomal PGE2 synthase (mPGES-1) has been developed based on the indole FLAP inhibitor MK-886. Compounds 23 and 30 inhibit mPGES-1 with potencies in the low nanomolar range and with selectivities of at least 100-fold compared to their inhibition of mPGES-2, thromboxane synthase and binding affinity to FLAP. They also block the production of PGE2 in cell based assays but with a decreased potency and more limited selectivity compared to the enzyme assays.

Human microsomal prostaglandin E synthase 1: a member of the MAPEG protein superfamily

In this chapter, we briefly review the MAPEG superfamily (membrane associated proteins in eicosanoid and glutathione metabolism), a family of proteins in which all human members except one possess glutathione conjugating capacity. Recent findings regarding the biological functions of MAPEG proteins are highlighted. More extensively, the characterization of human microsomal prostaglandin E synthase 1 is presented, including results and applied methodology.

mPGES-1 as a novel target for arthritis

PURPOSE OF REVIEW

Prostaglandin E2 (PGE2) is by far the major prostanoid synthesized in the joint and plays an important role in inflammation and pathogenesis of arthritis. Moreover, increased levels of PGE2 have been detected in serum and synovial fluids from arthritic patients. Little was known about the enzyme(s) involved in the isomerization of PGH2 into PGE2 synthesis until recent identification of PGE synthase (PGES). Several isoforms were characterized, among which microsomal PGES-1 (mPGES-1) has received much attention, because this enzyme is inducible and functionally linked with cyclooxygenase-2. This review focuses on recent findings regarding the regulation of mPGES-1 expression and the possible role of this enzyme in arthritis.

RECENT FINDINGS

Various in vitro and in vivo studies demonstrated that proinflammatory stimuli, such as interleukin-1beta and tumor necrosis factor-alpha upregulate the expression of mPGES-1 at the protein and mRNA level. Promoter analysis indicates that the transcription factor Egr-1 is involved in the positive regulation of mPGES-1. Studies from mPGES-1-deficient mice and animal models of inflammatory arthritis strongly suggest a role of mPGES-1 in the production of PGE2 and the pathogenesis of arthritis.

SUMMARY

This article reviews the regulation of mPGES-1 expression and provides evidence for a role of mPGES-1 in inducible PGE2 production and arthritis. Future studies using selective inhibitors of mPGES-1 activity or expression would clarify the role of this enzyme in arthritis.

Physiology and pharmacology of the prostaglandin J2 family

The prostaglandin (PG) J(2) family including PGJ(2), Delta(12)-PGJ(2), and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) are metabolites of PGD(2). They had been known as powerful inhibitors of cell proliferation and viral replication until 15d-PGJ(2) was found to be a natural ligand for peroxisome proliferator-activated receptor gamma (PPAR gamma). Since then, several new pharmacological actions of the PGJ(2) family have been found, such as pro- and anti-apoptotic effects, cell differentiation-inducing effects, and inhibitory effects on inflammatory processes, whether they depend on PPAR gamma or not. We reported that the PGJ(2) family, particularly 15d-PGJ(2), inhibits cell proliferation by reducing the expression of G(1) cyclins and inducing the expression of cyclin-dependent kinase inhibitor p21 and moreover, induces cell differentiation in vascular smooth muscle cells. In vascular endothelial cells, we found that 15d-PGJ(2) inhibits apoptotic cell death at least in part by the induction of the inhibitor of apoptosis protein c-IAP1. More importantly, physiological levels of laminar fluid shear stress loaded on endothelial cells upregulate the expression of lipocalin-type PGD(2) synthase, which converts PGH(2) to PGD(2), the precursor of the PGJ(2) family. Based on these results, we have hypothesized that the PGJ(2) family synthesized in vascular wall plays an important physiological role to protect vascular cells from atherogenic stimuli.

Use of cod liver oil during the first year of life is associated with lower risk of childhood-onset type 1 diabetes: a large, population-based, case-control study

BACKGROUND

In Norway, cod liver oil is an important source of dietary vitamin D and the long-chain n-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid, all of which have biological properties of potential relevance for the prevention of type 1 diabetes.

OBJECTIVE

The main objective was to investigate whether the use of dietary cod liver oil or other vitamin D supplements, either by the mother during pregnancy or by the child during the first year of life, is associated with a lower risk of type 1 diabetes among children.

DESIGN

We designed a nationwide case-control study in Norway with 545 cases of childhood-onset type 1 diabetes and 1668 population control subjects. Families were contacted by mail, and they completed a questionnaire on the frequency of use of cod liver oil and other vitamin D supplements and other relevant factors.

RESULTS

Use of cod liver oil in the first year of life was associated with a significantly lower risk of type 1 diabetes (adjusted odds ratio: 0.74; 95% CI: 0.56, 0.99). Use of other vitamin D supplements during the first year of life and maternal use of cod liver oil or other vitamin D supplements during pregnancy were not associated with type 1 diabetes.

CONCLUSION

Cod liver oil may reduce the risk of type 1 diabetes, perhaps through the antiinflammatory effects of long-chain n-3 fatty acids.

15-Deoxy-Δ12,14-prostaglandin J2 regulates the functional state and the survival of microglial cells through multiple molecular mechanisms

We have previously reported that rat primary microglial cultures express the nuclear receptor peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and that several functions associated with the activation of these cells, including nitric oxide (NO) and tumor necrosis factor-alpha synthesis, are down-regulated by 15-deoxy-delta12,14-prostaglandin J2 (15d-PGJ2) and ciglitazone, two specific PPAR-gamma agonists. Here we demonstrate that microglial cells not only express a functionally active PPAR-gamma, but also synthesize large amounts of 15d-PGJ2 upon stimulation with lipopolysaccharide (LPS). In addition, we show that, although 15d-PGJ2 and ciglitazone were equally effective in reducing microglial activation when used at 1-5 microm concentrations, 15d-PGJ2, but not of ciglitazone, reduced PGE2 production at low concentration (0.1 microm) and induced a time-dependent microglial impairment and apoptosis at high concentration (10 microm). Interestingly, the inhibition of PGE2 production was achieved mainly through the inhibition of cycloxygenase-2 enzymatic activity, as the expression of this enzyme and that of the microsomal isoform of PGE synthase remained unaltered. These findings suggest that 15d-PGJ2 affects the functional state and the survival of activated microglia through mechanisms only in part dependent on PPAR-gamma and that the concentration of 15d-PGJ2 is crucial in determining the particular microglial function affected.