Microsomal prostaglandin E synthase-1: the inducible synthase for prostaglandin E2

Kisspeptin signaling in astrocytes modulates the reproductive axis

Reproduction is safeguarded by multiple, often cooperative, regulatory networks. Kisspeptin signaling, via KISS1R, plays a fundamental role in reproductive control, primarily by regulation of hypothalamic GnRH neurons. We disclose herein a pathway for direct kisspeptin actions in astrocytes that contributes to central reproductive modulation. Protein-protein interaction and ontology analyses of hypothalamic proteomic profiles after kisspeptin stimulation revealed that glial/astrocyte markers are regulated by kisspeptin in mice. This glial-kisspeptin pathway was validated by the demonstrated expression of Kiss1r in mouse astrocytes in vivo and astrocyte cultures from humans, rats, and mice, where kisspeptin activated canonical intracellular signaling-pathways. Cellular coexpression of Kiss1r with the astrocyte markers GFAP and S100-β occurred in different brain regions, with higher percentage in Kiss1- and GnRH-enriched areas. Conditional ablation of Kiss1r in GFAP-positive cells in the G-KiR-KO mouse altered gene expression of key factors in PGE2 synthesis in astrocytes and perturbed astrocyte-GnRH neuronal appositions, as well as LH responses to kisspeptin and LH pulsatility, as surrogate marker of GnRH secretion. G-KiR-KO mice also displayed changes in reproductive responses to metabolic stress induced by high-fat diet, affecting female pubertal onset, estrous cyclicity, and LH-secretory profiles. Our data unveil a nonneuronal pathway for kisspeptin actions in astrocytes, which cooperates in fine-tuning the reproductive axis and its responses to metabolic stress.

Tumor cell senescence-induced macrophage CD73 expression is a critical metabolic immune checkpoint in the aging tumor microenvironment

Background: The role of senescent cells in the tumor microenvironment (TME) is usually bilateral, and diverse therapeutic approaches, such as radiotherapy and chemotherapy, can induce cellular senescence. Cellular interactions are widespread in the TME, and tumor cells reprogram immune cells metabolically by producing metabolites. However, how senescent cells remodel the metabolism of TME remains unclear. This study aimed to explore precise targets to enhance senescent cells-induced anti-tumor immunity from a metabolic perspective. Methods: The in vivo senescence model was induced by 8 Gy×3 radiotherapy or cisplatin chemotherapy, and the in vitro model was induced by 10 Gy-irradiation or cisplatin treatment. Metabonomic analysis and ELISA assay on tumor interstitial fluid were performed for metabolites screening. Marker expression and immune cell infiltration in the TME were analyzed by flow cytometry. Cell co-culture system and senescence-conditioned medium were used for crosstalk validation in vitro. RNA sequencing and rescue experiments were conducted for mechanism excavation. Immunofluorescence staining and single-cell transcriptome profiling analysis were performed for clinical validation. Results: We innovatively reveal the metabolic landscape of the senescent TME, characterized with the elevation of adenosine. It is attributed to the senescent tumor cell-induced CD73 upregulation of tumor-associated macrophages (TAMs). CD73 expression in TAMs is evoked by SASP-related pro-inflammatory cytokines, especially IL-6, and regulated by JAK/STAT3 pathway. Consistently, a positive correlation between tumor cells senescence and TAMs CD73 expression is identified in lung cancer clinical specimens and databases. Lastly, blocking CD73 in a senescent background suppresses tumors and activates CD8+ T cell-mediated antitumor immunity. Conclusions: TAMs expressed CD73 contributes significantly to the adenosine accumulation in the senescent TME, suggesting targeting CD73 is a novel synergistic anti-tumor strategy in the aging microenvironment.

The calcium-sensing receptor modulates the prostaglandin E2 pathway in intestinal inflammation

Introduction: The prostaglandin E2 (PGE2) pathway is one of the main mediators of intestinal inflammation. As activation of the calcium-sensing receptor (CaSR) induces expression of inflammatory markers in the colon, we assessed the impact of the CaSR on the PGE2 pathway regulation in colon cancer cells and the colon in vitro and in vivo. Methods and Results: We treated CaSR-transfected HT29 and Caco-2 colon cancer cell lines with different orthosteric ligands or modulators of the CaSR and measured gene expression and PGE2 levels. In CaSR-transfected HT29CaSR-GFP and Caco-2CaSR-GFP cells, the orthosteric CaSR ligand spermine and the positive allosteric CaSR modulator NPS R-568 both induced an inflammatory state as measured by IL-8 gene expression and significantly increased the expression of the PGE2 pathway key enzymes cyclooxygenase (COX)-2 and/or prostaglandin E2 synthase 1 (PGES-1). Inhibition of the CaSR with the calcilytic NPS 2143 abolished the spermine- and NPS R-568-induced pro-inflammatory response. Interestingly, we observed cell-line specific responses as e.g. PGES-1 expression was affected only in HT29CaSR-GFP but not in Caco-2CaSR-GFP cells. Other genes involved in the PGE2 pathway (COX-1, or the PGE2 receptors) were not responsive to the treatment. None of the studied genes were affected by any CaSR agonist in GFP-only transfected HT29GFP and Caco-2GFP cells, indicating that the observed gene-inducing effects of spermine and R-568 were indeed mediated by the CaSR. In vivo, we had previously determined that treatment with the clinically approved calcimimetic cinacalcet worsened symptoms in a dextran sulfate sodium (DSS)-induced colitis mouse model. In the colons of these mice, cinacalcet significantly induced gene expression of PGES-2 and the EP3 receptor, but not COX-2; while NPS 2143 increased the expression of the PGE2-degrading enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH). Importantly, neither treatment had any effect on the colons of non-DSS treated mice. Discussion: Overall, we show that activation of the CaSR induces the PGE2 pathway, albeit with differing effects in vitro and in vivo. This may be due to the different microenvironment in vivo compared to in vitro, specifically the presence of a CaSR-responsive immune system. Since calcilytics inhibit ligand-mediated CaSR signaling, they may be considered for novel therapies against inflammatory bowel disease.

Roles of tumor-associated macrophages in anti-PD-1/PD-L1 immunotherapy for solid cancers

In recent years, tumor immunotherapy has made significant progress. However, tumor immunotherapy, particularly immune checkpoint inhibitors (e.g., PD-1/PD-L1 inhibitors), benefits only a tiny proportion of patients in solid cancers. The tumor microenvironment (TME) acts a significant role in tumor immunotherapy. Studies reported that tumor-associated macrophages (TAMs), as one of the main components of TME, seriously affected the therapeutic effect of PD-1/PD-L1 inhibitors. In this review, we analyzed TAMs from epigenetic and single-cell perspectives and introduced the role and mechanisms of TAMs in anti-programmed death protein 1(anti-PD-1) therapy. In addition, we summarized combination regimens that enhance the efficacy of tumor PD-1/PD-L1 inhibitors and elaborated on the role of the TAMs in different solid cancers. Eventually, the clinical value of TAMs by influencing the therapeutic effect of tumor PD-1/PD-L1 inhibitors was discussed. These above are beneficial to elucidate poor therapeutic effect of PD-1/PD-L1 inhibitors in solid tumors from the point of view of TAMs and explore the strategies to improve its objective remission rate of solid cancers.

Analgesic effects of a highly selective mPGES-1 inhibitor

The growing opioid use and overdose crisis in the US is closely related to the abuse of pain medications. Particularly for postoperative pain (POP), ~ 310 million major surgeries are performed globally per year. Most patients undergoing surgical procedures experience acute POP, and ~ 75% of those with POP report the severity as moderate, severe, or extreme. Opioid analgesics are the mainstay for POP management. It is highly desirable to develop a truly effective and safe non-opioid analgesic to treat POP and other forms of pain. Notably, microsomal prostaglandin E2 (PGE₂) synthase-1 (mPGES-1) was once proposed as a potentially promising target for a next generation of anti-inflammatory drugs based on studies in mPGES-1 knockouts. However, to the best of our knowledge, no studies have ever been reported to explore whether mPGES-1 is also a potential target for POP treatment. In this study, we demonstrate for the first time that a highly selective mPGES-1 inhibitor can effectively relieve POP as well as other forms of pain through blocking the PGE₂ overproduction. All the data have consistently demonstrated that mPGES-1 is a truly promising target for treatment of POP as well as other forms of pain.

The specific deletion of cyclooxygenase-1 in megakaryocytes/platelets reduces intestinal polyposis in ApcMin/+ mice

Clinical and experimental evidence sustain the role of cyclooxygenase (COX)-1 in intestinal tumorigenesis. However, the cell type expressing the enzyme involved and molecular mechanism(s) have not been clarified yet. We aimed to elucidate the role of platelet COX-1 (the target of low-dose aspirin in humans) in intestinal tumorigenesis of ApcMin/+ mice, considered a clinically relevant model. To realize this objective, we generated an ApcMin/+ mouse with a specific deletion of Ptgs1(COX-1 gene name) in megakaryocytes/platelets (ApcMin/+;pPtgs1-/-mice) characterized by profound inhibition of thromboxane(TX)A2 biosynthesis ex vivo (serum TXB2; by 99%) and in vivo [urinary 2,3-dinor-TXB2(TXM), by 79%]. ApcMin/+ mice with the deletion of platelet COX-1 showed a significantly reduced number (67%) and size (32%) of tumors in the small intestine. The intestinal adenomas of these mice had decreased proliferative index associated with reduced COX-2 expression and systemic prostaglandin(PG)E2 biosynthesis (urinary PGEM) vs. ApcMin/+mice. Extravasated platelets were detected in the intestine of ApcMin/+mice. Thus, we explored their contribution to COX-2 induction in fibroblasts, considered the primary polyp cell type expressing the protein. In the coculture of human platelets and myofibroblasts, platelet-derived TXA2 was involved in the induction of COX-2-dependent PGE2 in myofibroblasts since it was prevented by the selective inhibition of platelet COX-1 by aspirin or by a specific antagonist of TXA2 receptors. In conclusion, our results support the platelet hypothesis of intestinal tumorigenesis and provide experimental evidence that selective inhibition of platelet COX-1 can mitigate early events of intestinal tumorigenesis by restraining COX-2 induction.

Structure-based screening for the discovery of 1,2,4-oxadiazoles as promising hits for the development of new anti-inflammatory agents interfering with eicosanoid biosynthesis pathways

The multiple inhibition of biological targets involved in pro-inflammatory eicosanoid biosynthesis represents an innovative strategy for treating inflammatory disorders in light of higher efficacy and safety. Herein, following a multidisciplinary protocol involving virtual combinatorial screening, chemical synthesis, and in vitro and in vivo validation of the biological activities, we report the identification of 1,2,4-oxadiazole-based eicosanoid biosynthesis multi-target inhibitors. The multidisciplinary scientific approach led to the identification of three 1,2,4-oxadiazole hits (compounds 1, 2 and 5), all endowed with IC₅₀ values in the low micromolar range, acting as 5-lipoxygenase-activating protein (FLAP) antagonists (compounds 1 and 2), and as a multi-target inhibitor (compound 5) of arachidonic acid cascade enzymes, namely cyclooxygenase-1 (COX-1), 5-lipoxygenase (5-LO) and microsomal prostaglandin E₂ synthase-1 (mPGES-1). Moreover, our in vivo results demonstrate that compound 5 is able to attenuate leukocyte migration in a model of zymosan-induced peritonitis and to modulate the production of IL-1β and TNF-α. These results are of interest for further expanding the chemical diversity around the 1,2,4-oxadiazole central core, enabling the identification of novel anti-inflammatory agents characterized by a favorable pharmacological profile and considering that moderate interference with multiple targets might have advantages in re-adjusting homeostasis.

Composition and Acute Inflammatory Response from Tetraponera rufonigra Venom on RAW 264.7 Macrophage Cells

Tetraponera rufonigra (Arboreal Bicoloured Ant) venom induces pain, inflammation, and anaphylaxis in people and has an increased incident in Southeast Asia regions. The bioactive components and mechanism of action of the ant venom are still limited. The aim of this research was to identify the protein composition and inflammatory process of the ant venom by using RAW 264.7 macrophage cells. The major venom proteins are composed of 5' nucleotidase, prolyl endopeptidase-like, aminopeptidase N, trypsin-3, venom protein, and phospholipase A₂ (PLA₂). The venom showed PLA₂ activity and represented 0.46 μg of PLA₂ bee venom equivalent/μg crude venom protein. The venom induced cytotoxic in a dose- and time-dependent manner with IC₂₀ approximately at 4.01 µg/mL. The increased levels of COX-2 and PGE₂ were observed after 1 h of treatment correlating with an upregulation of COX-2 expression. Moreover, the level of mPGES-1 expression was obviously increased after 12 h of venom induction. Hence, our results suggested that the induction of COX-2/mPGEs-1 pathway could be a direct pathway for the ant venom-induced inflammation.

Clinical data mining reveals analgesic effects of lapatinib in cancer patients

Microsomal prostaglandin E2 synthase 1 (mPGES-1) is recognized as a promising target for a next generation of anti-inflammatory drugs that are not expected to have the side effects of currently available anti-inflammatory drugs. Lapatinib, an FDA-approved drug for cancer treatment, has recently been identified as an mPGES-1 inhibitor. But the efficacy of lapatinib as an analgesic remains to be evaluated. In the present clinical data mining (CDM) study, we have collected and analyzed all lapatinib-related clinical data retrieved from clinicaltrials.gov. Our CDM utilized a meta-analysis protocol, but the clinical data analyzed were not limited to the primary and secondary outcomes of clinical trials, unlike conventional meta-analyses. All the pain-related data were used to determine the numbers and odd ratios (ORs) of various forms of pain in cancer patients with lapatinib treatment. The ORs, 95% confidence intervals, and P values for the differences in pain were calculated and the heterogeneous data across the trials were evaluated. For all forms of pain analyzed, the patients received lapatinib treatment have a reduced occurrence (OR 0.79; CI 0.70–0.89; P = 0.0002 for the overall effect). According to our CDM results, available clinical data for 12,765 patients enrolled in 20 randomized clinical trials indicate that lapatinib therapy is associated with a significant reduction in various forms of pain, including musculoskeletal pain, bone pain, headache, arthralgia, and pain in extremity, in cancer patients. Our CDM results have demonstrated the significant analgesic effects of lapatinib, suggesting that lapatinib may be repurposed as a novel type of analgesic.

The Biosynthesis of Enzymatically Oxidized Lipids

Enzymatically oxidized lipids are a specific group of biomolecules that function as key signaling mediators and hormones, regulating various cellular and physiological processes from metabolism and cell death to inflammation and the immune response. They are broadly categorized as either polyunsaturated fatty acid (PUFA) containing (free acid oxygenated PUFA "oxylipins", endocannabinoids, oxidized phospholipids) or cholesterol derivatives (oxysterols, steroid hormones, and bile acids). Their biosynthesis is accomplished by families of enzymes that include lipoxygenases (LOX), cyclooxygenases (COX), cytochrome P450s (CYP), and aldo-keto reductases (AKR). In contrast, non-enzymatically oxidized lipids are produced by uncontrolled oxidation and are broadly considered to be harmful. Here, we provide an overview of the biochemistry and enzymology of LOXs, COXs, CYPs, and AKRs in humans. Next, we present biosynthetic pathways for oxylipins, oxidized phospholipids, oxysterols, bile acids and steroid hormones. Last, we address gaps in knowledge and suggest directions for future work.

Heracleum moellendorffii roots inhibit the production of pro-inflammatory mediators through the inhibition of NF-κB and MAPK signaling, and activation of ROS/Nrf2/HO-1 signaling in LPS-stimulated RAW264.7 cells

BACKGROUND

Heracleum moellendorffii roots (HM-R) have been long treated for inflammatory diseases such as arthritis, backache and fever. However, an anti-inflammatory effect and the specific mechanism of HM-R were not yet clear. In this study, we for the first time explored the anti-inflammatory of HM-R.

METHODS

The cytotoxicity of HM-R against RAW264.7 cells was evaluated using MTT assay. The inhibition of NO and PGE₂ production by HM-R was evaluated using Griess reagent and Prostaglandin E₂ ELISA Kit, respectively. The changes in mRNA or protein level following HM-R treatment were assessed by RT-PCR and Western blot analysis, respectively.

RESULTS

HM-R dose-dependently blocked LPS-induced NO and PGE₂ production. In addition, HM-R inhibited LPS-induced overexpression of iNOS, COX-2, IL-1β and IL-6 in RAW264.7 cells. HM-R inhibited LPS-induced NF-κB signaling activation through blocking IκB-α degradation and p65 nuclear accumulation. Furthermore, HM-R inhibited MAPK signaling activation by attenuating the phosphorylation of ERK1/2, p38 and JNK. HM-R increased nuclear accumulation of Nrf2 and HO-1 expression. However, NAC reduced the increased nuclear accumulation of Nrf2 and HO-1 expression by HM-R. In HPLC analysis, falcarinol was detected from HM-R as an anti-inflammatory compound.

CONCLUSIONS

These results indicate that HM-R may exert anti-inflammatory activity by inhibiting NF-κB and MAPK signaling, and activating ROS/Nrf2/HO-1 signaling. These findings suggest that HM-R has a potential as a natural material for the development of anti-inflammatory drugs.

Transcriptomic studies provide insights into the tumor suppressive role of miR-146a-5p in non-small cell lung cancer (NSCLC) cells

Non-small cell lung cancer (NSCLC) is a complex disease in need of new methods of therapeutic intervention. Recent interest has focused on using microRNAs (miRNAs) as a novel treatment method for various cancers. miRNAs negatively regulate gene expression post-transcriptionally, and have become attractive candidates for cancer treatment because they often simultaneously target multiple genes of similar biological function. One such miRNA is miR-146a-5p, which has been described as a tumor suppressive miRNA in NSCLC cell lines and tissues. In this study, we performed RNA-Sequencing (RNA-Seq) analysis following transfection of synthetic miR-146a-5p in an NSCLC cell line, A549, and validated our data with Gene Ontology and qRT-PCR analysis of known miR-146a-5p target genes. Our transcriptomic data revealed that miR-146a-5p exerts its tumor suppressive function beyond previously reported targeting of EGFR and NF-κB signaling. miR-146a-5p mimic transfection downregulated arachidonic acid metabolism genes, the RNA-binding protein HuR, and many HuR-stabilized pro-cancer mRNAs, including TGF-β, HIF-1α, and various cyclins. miR-146a-5p transfection also reduced expression and cellular release of the chemokine CCL2, and this effect was mediated through the 3' untranslated region of its mRNA. Taken together, our work reveals that miR-146a-5p functions as a tumor suppressor in NSCLC by controlling various metabolic and signaling pathways through direct and indirect mechanisms.

CRISPR/Cas9-based liver-derived reporter cells for screening of mPGES-1 inhibitors

mPGES-1 is a terminal rate-limiting enzyme responsible for inflammation-induced PGE2 production. The inhibition of mPGES-1 has been considered as a safe and effective target for the treatment of inflammation and cancer. However, a specific, efficient, and simple method for high-throughput screening of mPGES-1 inhibitors is still lacking. In this study, we developed a fluorescence imaging strategy to monitor the expression of mPGES-1 via CRISPR/Cas9 knock-in system. Immunofluorescence colocalisation, Sanger sequencing, RNAi, and IL-1β treatment all confirmed the successful construction of mPGES-1 reporter cells. The fluorescence signal intensity of the reporter cells treated with four conventional mPGES-1 inhibitors was considerably attenuated via flow cytometry and fluorescent microplate reader, demonstrating that the reporter cells can be used as an efficient and convenient means for screening and optimising mPGES-1 inhibitors. Moreover, it provides a new technical support for the development of targeted small molecule compounds for anti-inflammatory and tumour therapy.

mPGES-1 and ALOX5/-15 in tumor-associated macrophages

The tumor immune landscape gained considerable interest based on the knowledge that genetic aberrations in cancer cells alone are insufficient for tumor development. Macrophages are basically supporting all hallmarks of cancer and owing to their tremendous plasticity they may exert a whole spectrum of anti-tumor and pro-tumor activities. As part of the innate immune response, macrophages are armed to attack tumor cells, alone or in concert with distinct T cell subsets. However, in the tumor microenvironment, they sense nutrient and oxygen gradients, receive multiple signals, and respond to this incoming information with a phenotype shift. Often, their functional output repertoire is shifted to become tumor-supportive. Incoming and outgoing signals are chemically heterogeneous but also comprise lipid mediators. Here, we review the current understanding whereby arachidonate metabolites derived from the cyclooxygenase and lipoxygenase pathways shape the macrophage phenotype in a tumor setting. We discuss these findings in the context of cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1) expression and concomitant prostaglandin E₂ (PGE₂) formation. We elaborate the multiple actions of this lipid in affecting macrophage biology, which are sensors for and generators of this lipid. Moreover, we summarize properties of 5-lipoxygenases (ALOX5) and 15-lipoxygenases (ALOX15, ALOX15B) in macrophages and clarify how these enzymes add to the role of macrophages in a dynamically changing tumor environment. This review will illustrate the potential routes how COX-2/mPGES-1 and ALOX5/-15 in macrophages contribute to the development and progression of a tumor.

Aminothiazoles inhibit osteoclastogenesis and PGE2 production in LPS-stimulated co-cultures of periodontal ligament and RAW 264.7 cells, and RANKL-mediated osteoclastogenesis and bone resorption in PBMCs

Inflammatory mediator prostaglandin E₂ (PGE₂ ) contributes to bone resorption in several inflammatory conditions including periodontitis. The terminal enzyme, microsomal prostaglandin E synthase-1 (mPGES-1) regulating PGE₂ synthesis is a promising therapeutic target to reduce inflammatory bone loss. The aim of this study was to investigate effects of mPGES-1 inhibitors, aminothiazoles TH-848 and TH-644, on PGE₂ production and osteoclastogenesis in co-cultures of periodontal ligament (PDL) and osteoclast progenitor cells RAW 264.7, stimulated by lipopolysaccharide (LPS), and bone resorption in RANKL-mediated peripheral blood mononuclear cells (PBMCs). PDL and RAW 264.7 cells were cultured separately or co-cultured and treated with LPS alone or in combination with aminothiazoles. Multinucleated cells stained positively for tartrate-resistant acid phosphatase (TRAP) were scored as osteoclast-like cells. Levels of PGE₂ , osteoprotegerin (OPG) and interleukin-6, as well as mRNA expression of mPGES-1, OPG and RANKL were analysed in PDL cells. PBMCs were treated with RANKL alone or in combination with aminothiazoles. TRAP-positive multinucleated cells were analysed and bone resorption was measured by the CTX-I assay. Aminothiazoles reduced LPS-stimulated osteoclast-like cell formation both in co-cultures and in RAW 264.7 cells. Additionally, aminothiazoles inhibited PGE₂ production in LPS-stimulated cultures, but did not affect LPS-induced mPGES-1, OPG or RANKL mRNA expression in PDL cells. In PBMCs, inhibitors decreased both osteoclast differentiation and bone resorption. In conclusion, aminothiazoles reduced the formation of osteoclast-like cells and decreased the production of PGE₂ in co-cultures as well as single-cell cultures. Furthermore, these compounds inhibited RANKL-induced bone resorption and differentiation of PBMCs, suggesting these inhibitors for future treatment of inflammatory bone loss such as periodontitis.

Raging the War Against Inflammation With Natural Products

Over the last few decade Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) are the drugs of choice for treating numerous inflammatory diseases including rheumatoid arthritis. The NSAIDs produces anti-inflammatory activity via inhibiting cyclooxygenase enzyme, responsible for the conversation of arachidonic acid to prostaglandins. Likewise, cyclooxegenase-2 inhibitors (COX-2) selectively inhibit the COX-2 enzyme and produces significant anti-inflammatory, analgesic, and anti-pyretic activity without producing COX-1 associated gastrointestinal and renal side effects. In last two decades numerous selective COX-2 inhibitors (COXIBs) have been developed and approved for various inflammatory conditions. However, data from clinical trials have suggested that the prolong use of COX-2 inhibitors are also associated with life threatening cardiovascular side effects including ischemic heart failure and myocardial infection. In these scenario secondary metabolites from natural product offers a great hope for the development of novel anti-inflammatory compounds. Although majority of the natural product based compounds exhibit more selectively toward COX-1. However, the data suggest that slight structural modification can be helpful in developing COX-2 selective secondary metabolites with comparative efficacy and limited side effects. This review is an effort to highlight the secondary metabolites from terrestrial and marine source with significant COX-2 and COX-2 mediated PGE2 inhibitory activity, since it is anticipated that isolates with ability to inhibit COX-2 mediated PGE2 production would be useful in suppressing the inflammation and its classical sign and symptoms. Moreover, this review has highlighted the potential lead compounds including berberine, kaurenoic acid, α-cyperone, curcumin, and zedoarondiol for further development with the help of structure-activity relationship (SAR) studies and their current status.

Activation of Nrf2/HO-1 Pathway by Nardochinoid C Inhibits Inflammation and Oxidative Stress in Lipopolysaccharide-Stimulated Macrophages

The roots and rhizomes of Nardostachys chinensis have neuroprotection and cardiovascular protection effects. However, the specific mechanism of N. chinensis is not yet clear. Nardochinoid C (DC) is a new compound with new skeleton isolated from N. chinensis and this study for the first time explored the anti-inflammatory and anti-oxidant effect of DC. The results showed that DC significantly reduced the release of nitric oxide (NO) and prostaglandin E₂ (PGE₂) in lipopolysaccharide (LPS)-activated RAW264.7 cells. The expression of pro-inflammatory proteins including inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) were also obviously inhibited by DC in LPS-activated RAW264.7 cells. Besides, the production of interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were also remarkably inhibited by DC in LPS-activated RAW264.7 cells. DC also suppressed inflammation indicators including COX-2, PGE₂, TNF-α, and IL-6 in LPS-stimulated THP-1 macrophages. Furthermore, DC inhibited the macrophage M1 phenotype and the production of reactive oxygen species (ROS) in LPS-activated RAW264.7 cells. Mechanism studies showed that DC mainly activated nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, increased the level of anti-oxidant protein heme oxygenase-1 (HO-1) and thus produced the anti-inflammatory and anti-oxidant effects, which were abolished by Nrf2 siRNA and HO-1 inhibitor. These findings suggested that DC could be a new Nrf2 activator for the treatment and prevention of diseases related to inflammation and oxidative stress.

Suppressing mPGES-1 expression by sinomenine ameliorates inflammation and arthritis

Recently, microsomal prostaglandin E synthase 1 (mPGES-1) has attracted much attention from pharmacologists as a promising strategy and an attractive target for treating various types of diseases including rheumatoid arthritis (RA), which could preserve the anti-inflammatory effect while reducing the adverse effects often occur during administration of non-steroidal anti-inflammatory drugs (NSAIDs). Here, we report that sinomenine (SIN) decreased prostaglandin (PG)E₂ levels without affecting prostacyclin (PG)I₂ and thromboxane (TX)A₂ synthesis via selective inhibiting mPGES-1 expression, a possible reason of low risk of cardiovascular event compared with NSAIDs. In addition, mPGES-1 protein expression was down-regulated by SIN treatment in the inflamed paw tissues both in carrageenan-induced edema model in rats and the collagen-II induced arthritis (CIA) model in DBA mice. More interestingly, SIN suppressed the last step of mPGES-1 gene expression by decreasing the DNA binding ability of NF-κB, paving a new way for drug discovery.

Curbing tumorigenesis and malignant progression through the pharmacological control of the wound healing process

The prevention of cancer development and its progression is an urgent unmet medical need. Novel knowledge on the biology of cancer has evidenced that genetic changes occurring within cancer cells contribute, but are not sufficient, for tumor promotion and progression. The results of clinical studies and experimental animal models have suggested pursuing new avenues for the prevention of cancer development in the early stages, by using drugs that modulate platelet responses and those interfering with the synthesis and action of the mediators of inflammation. In fact, malignant tumors often develop at sites of chronic injury associated with platelet activation and chronic inflammation. In this review, we cover the evidence supporting this hypothesis and the rationale for the pharmacological treatment with antiplatelet agents, including low-dose aspirin, and antiinflammatory drugs to curb tumorigenesis and malignant progression. The evidence for a chemopreventive effect of low-dose aspirin against colorectal cancer (CRC) has been recently found appropriate by the U.S. Preventive Services Task Force, which recommends the use of the drug for primary prevention of cardiovascular disease and CRC.

Stauntoside B inhibits macrophage activation by inhibiting NF-κB and ERK MAPK signalling

Inflammation is a defensive reaction of body to resist foreign invasion. However, it has been demonstrated that excessive and continuous inflammatory responses contribute to various inflammatory diseases, including rheumatoid arthritis. Nuclear factor-κB (NF-κB) regulates the expression of an array of inflammatory mediators, cytokines and chemokine genes in activated macrophages. Therefore, NF-κB has become an attractive drug target for controlling inflammation. In this study, stauntoside B, a C21 steroidal glycosides compound isolated from a Chinese medicine Cynanchi Stauntonii, was for the first time found to suppress macrophage activation induced by lipopolysaccharide (LPS) in RAW264.7 cells and rat primary peritoneal macrophages and could be a potent NF-κB inhibitor. The results showed that stauntoside B significantly reduced the release of inflammatory mediators in activated RAW264.7 cells and rat peritoneal macrophages, including nitric oxide (NO) and prostaglandin E2 (PGE2). The mRNA expressions of pro-inflammatory mediators and cytokines, including inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), microsomal prostaglandin synthetase-1 (mPGES-1), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), and monocyte chemoattractant protein-1 (MCP-1) as well as the production of TNF-α and IL-6 were also inhibited by stauntoside B. Mechanistic investigation implies that the anti-inflammatory activity of stauntoside B could result from the suppression of LPS-induced IKKα/β activation, IκBα phosphorylation, p65 (ser536) NF-κB phosphorylation, and ERK MAPK activation by stauntoside B treatment in activated macrophages. Meanwhile, stauntoside B could induce apoptosis in LPS-activated macrophages. The current study suggests stauntoside B being a valuable candidate drug for the treatment of inflammatory diseases, especially for NF-κB activation associated inflammatory diseases.

Antiinflammatory effects of essential oil from the leaves of Cinnamomum cassia and cinnamaldehyde on lipopolysaccharide-stimulated J774A.1 cells

Cassia oil (CO) from different parts of Cinnamomum cassia have different active components. Very few pharmacological properties of cassia leaf oil have been reported. This study investigated and compared effects of cassia leaf oil and cinnamaldehyde on lipopolysaccharide (LPS)-activated J774A.1 cells. Volatile compositions in cassia leaf oil were identified by gas chromatography-mass spectrometry (MS)/MS. Effects of CO and cinnamaldehyde on LPS-activated J774A.1 cells were investigated by determining nitric oxide (NO) production using Griess reaction assay; expression of pro-inflammatory cytokines, enzymes involve in inflammatory mediators; antiinflammatory cytokines, and iron exporter ferroportin1 (Fpn1) using reverse transcription-polymerase chain reaction; and production of tumor necrosis factor (TNF-α) and interleukin (IL)-10 using ELISA. The main component of CO was cinnamaldehyde. Both oils at 1-20 μg/ml markedly inhibited NO production in LPS-activated J774A.1 cells with IC50 value of 6.1 ± 0.25 and 9.97 ± 0.35 μg/ml, respectively. They similarly inhibited mRNA expression of pro-inflammatory cytokines and chemokines. These mediators included TNF-α, IL-1β, IL-6, monocyte chemoattractant protein-1, and macrophage inflammatory protein-1α in LPS-activated cells. They also significantly decreased expression of inducible enzymes inducible nitric oxide synthase, cyclooxygenase-2, microsomal prostaglandin-E synthase-1. In the opposite way, they increased mRNA expression and the production of antiinflammatory cytokines IL-10 and transforming growth factor-β. In addition, they promoted the expression of Fpn1. These results demonstrated that inhibitory effects of cassia leaf oil from C. cassia mainly came from cinnamaldehyde. This compound not only inhibited inflammatory mediators but also activated antiinflammatory mediators in LPS-activated J774A.1 cells. It may also have an effect on iron regulatory proteins in activated macrophages.

Prostaglandin E2 produced by inducible COX-2 and mPGES-1 promoting cancer cell proliferation in vitro and in vivo

AIM

Many cancers originate and flourish in a prolonged inflammatory environment. Our aim is to understand the mechanisms of how the pathway of prostaglandin E2 (PGE2) biosynthesis and signaling can promote cancer growth in inflammatory environment at cellular and animal model levels.

MAIN METHODS

In this study, a chronic inflammation pathway was mimicked with a stable cell line that over-expressed a novel human enzyme consisting of cyclooxygenase isoform-2 (COX-2) linked to microsomal (PGE2 synthase-1 (mPGES-1)) for the overproduction of pathogenic PGE2. This PGE2-producing cell line was co-cultured and co-implanted with three human cancer cell lines including prostate, lung, and colon cancers in vitro and in vivo, respectively.

KEY FINDINGS

Increases in cell doubling rates for the three cancer cell types in the presence of the PGE2-producing cell line were clearly observed. In addition, one of the four human PGE2 subtype receptors, EP1, was used as a model to identify PGE2-signaling involved in promoting the cancer cell growth. This finding was further proven in vivo by co-implanting the PGE2-producing cells line and the EP1-positive cancer cells into the immune deficient mice, after that, it was observed that the PGE2-producing cells promoted all three types of cancer formation in the mice.

SIGNIFICANCE

This study clearly demonstrated that the human COX-2 linked to mPGES-1 is a pathway that, when mediated by the EP, is linked to promoting cancer growth in a chronic inflammatory environment. The identified pathway could be used as a novel target for developing and advancing anti-inflammation and anti-cancer interventions.

Benzo[d]isothiazole 1,1-dioxide derivatives as dual functional inhibitors of 5-lipoxygenase and microsomal prostaglandin E(2) synthase-1

A series of 6-nitro-3-(m-tolylamino) benzo[d]isothiazole 1,1-dioxide analogues were synthesized and evaluated for their inhibition activity against 5-lipoxygenase (5-LOX) and microsomal prostaglandin E2 synthase (mPGES-1). These compounds can inhibit both enzymes with IC50 values ranging from 0.15 to 23.6μM. One of the most potential compounds, 3g, inhibits 5-LOX and mPGES-1 with IC50 values of 0.6μM, 2.1μM, respectively.

Anti-inflammatory properties of prostaglandin E2: deletion of microsomal prostaglandin E synthase-1 exacerbates non-immune inflammatory arthritis in mice

Prostanoids and PGE2 in particular have been long viewed as one of the major mediators of inflammation in arthritis. However, experimental data indicate that PGE2 can serve both pro- and anti-inflammatory functions. We have previously shown (Kojima et al., J. Immunol. 180 (2008) 8361-8368) that microsomal prostaglandin E synthase-1 (mPGES-1) deletion, which regulates PGE2 production, resulted in the suppression of collagen-induced arthritis (CIA) in mice. This suppression was attributable, at least in part, to the impaired generation of type II collagen autoantibodies. In order to examine the function of mPGES-1 and PGE2 in a non-autoimmune form of arthritis, we used the collagen antibody-induced arthritis (CAIA) model in mice deficient in mPGES-1, thereby bypassing the engagement of the adaptive immune response in arthritis development. Here we report that mPGES-1 deletion significantly increased CAIA disease severity. The latter was associated with a significant (~3.6) upregulation of neutrophil, but not macrophage, recruitment to the inflamed joints. The lipidomic analysis of the arthritic mouse paws by quantitative liquid chromatography/tandem mass-spectrometry (LC/MS/MS) revealed a dramatic (~59-fold) reduction of PGE2 at the peak of arthritis. Altogether, this study highlights mPGES-1 and its product PGE2 as important negative regulators of neutrophil-mediated inflammation and suggests that specific mPGES-1 inhibitors may have differential effects on different types of inflammation. Furthermore, neutrophil-mediated diseases could be exacerbated by inhibition of mPGES-1.

Mechanistic aspects of COX-2 expression in colorectal neoplasia

The cyclooxygenase-2 (COX-2) enzyme catalyzes the rate-limiting step of prostaglandin formation in pathogenic states and a large amount of evidence has demonstrated constitutive COX-2 expression to be a contributing factor promoting colorectal cancer (CRC). Various genetic, epigenetic, and inflammatory pathways have been identified to be involved in the etiology and development of CRC. Alteration in these pathways can influence COX-2 expression at multiple stages of colon carcinogenesis allowing for elevated prostanoid biosynthesis to occur in the tumor microenvironment. In normal cells, COX-2 expression levels are potently regulated at the post-transcriptional level through various RNA sequence elements present within the mRNA 3' untranslated region (3'UTR). A conserved AU-rich element (ARE) functions to target COX-2 mRNA for rapid decay and translational inhibition through association with various RNA-binding proteins to influence the fate of COX-2 mRNA. Specific microRNAs (miRNAs) bind regions within the COX-2 3'UTR and control COX-2 expression. In this chapter, we discuss novel insights in the mechanisms of altered post-transcriptional regulation of COX-2 in CRC and how this knowledge may be used to develop novel strategies for cancer prevention and treatment.

Stimulation of fat accumulation in hepatocytes by PGE₂-dependent repression of hepatic lipolysis, β-oxidation and VLDL-synthesis

Hepatic steatosis is recognized as hepatic presentation of the metabolic syndrome. Hyperinsulinaemia, which shifts fatty acid oxidation to de novo lipogenesis and lipid storage in the liver, appears to be a principal elicitor particularly in the early stages of disease development. The impact of PGE₂, which has previously been shown to attenuate insulin signaling and hence might reduce insulin-dependent lipid accumulation, on insulin-induced steatosis of hepatocytes was studied. The PGE₂-generating capacity was enhanced in various obese mouse models by the induction of cyclooxygenase 2 and microsomal prostaglandin E-synthases (mPGES1, mPGES2). PGE₂ attenuated the insulin-dependent induction of SREBP-1c and its target genes glucokinase and fatty acid synthase. Nevertheless, PGE₂ enhanced incorporation of glucose into hepatic triglycerides synergistically with insulin. This was most likely due to a combination of a PGE₂-dependent repression of (1) the key lipolytic enzyme adipose triglyceride lipase, (2) carnitine-palmitoyltransferase 1, a key regulator of mitochondrial β-oxidation, and (3) microsomal transfer protein, as well as (4) apolipoprotein B, key components of the VLDL synthesis. Repression of PGC1α, a common upstream regulator of these genes, was identified as a possible cause. In support of this hypothesis, overexpression of PGC1α completely blunted the PGE₂-dependent fat accumulation. PGE₂ enhanced lipid accumulation synergistically with insulin, despite attenuating insulin signaling and might thus contribute to the development of hepatic steatosis. Induction of enzymes involved in PGE₂ synthesis in in vivo models of obesity imply a potential role of prostanoids in the development of NAFLD and NASH.

Prostaglandin E2 blocks menadione-induced apoptosis through the Ras/Raf/Erk signaling pathway in promonocytic leukemia cell lines

Altered oxidative stress has long been observed in cancer cells, and this biochemical property of cancer cells represents a specific vulnerability that can be exploited for therapeutic benefit. The major role of an elevated oxidative stress for the efficacy of molecular targeted drugs is under investigation. Menadione is considered an attractive model for the study of oxidative stress, which can induce apoptosis in human leukemia HL-60 cell lines. Prostaglandin E(2) (PGE(2)) via its receptors not only promotes cell survival but also reverses apoptosis and promotes cancer progression. Here, we present evidence for the biological role of PGE(2) as a protective agent of oxidative stress-induced apoptosis in monocytic cells. Pretreatment of HL-60 cells with PGE(2) markedly ameliorated the menadione-induced apoptosis and inhibited the degradation of PARP and lamin B. The EP(2) receptor antagonist AH6809 abrogated the inhibitory effect of PGE(2), suggesting the role of the EP(2)/cAMP system. The PKA inhibitor H89 also reversed apoptosis and decreased the PKA activity that was elevated 10-fold by PGE(2). The treatment of HL-60 cells with NAC or zinc chloride showed a similar protective effect as with PGE(2) on menadione-treated cells. Furthermore, PGE(2) activated the Ras/Raf/MEK pathway, which in turn initiated ERK activation, and ultimately protected menadione-induced apoptosis. These results imply that PGE(2) via cell survival pathways may protect oxidative stress-induced apoptosis in monocytic cells. This study warrants further pre-clinical investigation as well as application towards leukemia clinics.

Prostaglandins in cancer cell adhesion, migration, and invasion

Prostaglandins exert a profound influence over the adhesive, migratory, and invasive behavior of cells during the development and progression of cancer. Cyclooxygenase-2 (COX-2) and microsomal prostaglandin E₂ synthase-1 (mPGES-1) are upregulated in inflammation and cancer. This results in the production of prostaglandin E₂ (PGE₂), which binds to and activates G-protein-coupled prostaglandin E_1–4 receptors (EP_1–4). Selectively targeting the COX-2/mPGES-1/PGE₂/EP_1–4 axis of the prostaglandin pathway can reduce the adhesion, migration, invasion, and angiogenesis. Once stimulated by prostaglandins, cadherin adhesive connections between epithelial or endothelial cells are lost. This enables cells to invade through the underlying basement membrane and extracellular matrix (ECM). Interactions with the ECM are mediated by cell surface integrins by “outside-in signaling” through Src and focal adhesion kinase (FAK) and/or “inside-out signaling” through talins and kindlins. Combining the use of COX-2/mPGES-1/PGE₂/EP_1–4 axis-targeted molecules with those targeting cell surface adhesion receptors or their downstream signaling molecules may enhance cancer therapy.

Aging-shifted prostaglandin profile in endothelium as a factor in cardiovascular disorders

Age-associated endothelium dysfunction is a major risk factor for the development of cardiovascular diseases. Endothelium-synthesized prostaglandins and thromboxane are local hormones, which mediate vasodilation and vasoconstriction and critically maintain vascular homeostasis. Accumulating evidence indicates that the age-related changes in endothelial eicosanoids contribute to decline in endothelium function and are associated with pathological dysfunction. In this review we summarize currently available information on aging-shifted prostaglandin profiles in endothelium and how these shifts are associated with cardiovascular disorders, providing one molecular mechanism of age-associated endothelium dysfunction and cardiovascular diseases.

MK886 inhibits the proliferation of HL-60 leukemia cells by suppressing the expression of mPGES-1 and reducing prostaglandin E2 synthesis

Microsomal prostaglandin E synthase-1 (mPGES-1), an inducible enzyme that specifically catalyzes the conversion of prostaglandin H2 (PGH2) to prostaglandin E2 (PGE2), has been reported to be over-expressed in a variety of solid tumor cells and tissues, but not in normal tissues. Its association with leukemia, however, has not been fully investigated. Our study revealed, for the first time, that mPGES-1 is over-expressed in human acute myeloid leukemia HL-60 cells. Cytotoxicity assays and flow cytometry showed that MK886, an inhibitor of mPGES-1, inhibits proliferation of HL-60 cells and induces apoptosis in a dose- and time-dependent manner, which may result from down-regulation of mPGES-1 expression and PGE2 synthesis. Evaluation of mediators of apoptotic signaling revealed up-regulation of BAX expression and caspase-3 activity, as well as significant decreases in Bcl2 and P-Akt. We conclude that MK886 reduces the viability of leukemia HL-60 cells by reducing mPGES-1 expression and PGE2 synthesis in a dose-dependent manner, which strongly suggests that mPGES-1 inhibitors should be considered as promising candidates for leukemia treatment.

Prostaglandin E2 and T cells: friends or foes?

Our understanding of the key players involved in the differential regulation of T-cell responses during inflammation, infection and auto-immunity is fundamental for designing efficient therapeutic strategies against immune diseases. With respect to this, the inhibitory role of the lipid mediator prostaglandin E₂ (PGE₂) in T-cell immunity has been documented since the 1970s. Studies that ensued investigating the underlying mechanisms substantiated the suppressive function of micromolar concentrations of PGE₂ in T-cell activation, proliferation, differentiation and migration. However, the past decade has seen a revolution in this perspective, since nanomolar concentrations of PGE₂ have been shown to potentiate Th1 and Th17 responses and aid in T-cell proliferation. The understanding of concentration-specific effects of PGE₂ in other cell types, the development of mice deficient in each subtype of the PGE₂ receptors (EP receptors) and the delineation of signalling pathways mediated by the EP receptors have enhanced our understanding of PGE₂ as an immune-stimulator. PGE₂ regulates a multitude of functions in T-cell activation and differentiation and these effects vary depending on the micro-environment of the cell, maturation and activation state of the cell, type of EP receptor involved, local concentration of PGE₂ and whether it is a homeostatic or inflammatory scenario. In this review, we compartmentalize the various aspects of this complex relationship of PGE₂ with T lymphocytes. Given the importance of this molecule in T-cell activation, we also address the possibility of using EP receptor antagonism as a potential therapeutic approach for some immune disorders.

Boswellia serrata: an overall assessment of in vitro, preclinical, pharmacokinetic and clinical data

Non-steroidal anti-inflammatory drug (NSAID) intake is associated with high prevalence of gastrointestinal or cardiovascular adverse effects. All efforts to develop NSAIDs that spare the gastrointestinal tract and the cardiovasculature are still far from achieving a breakthrough. In the last two decades, preparations of the gum resin of Boswellia serrata (a traditional ayurvedic medicine) and of other Boswellia species have experienced increasing popularity in Western countries. Animal studies and pilot clinical trials support the potential of B. serrata gum resin extract (BSE) for the treatment of a variety of inflammatory diseases like inflammatory bowel disease, rheumatoid arthritis, osteoarthritis and asthma. Moreover, in 2002 the European Medicines Agency classified BSE as an 'orphan drug' for the treatment of peritumoral brain oedema. Compared to NSAIDs, it is expected that the administration of BSE is associated with better tolerability, which needs to be confirmed in further clinical trials. Until recently, the pharmacological effects of BSE were mainly attributed to suppression of leukotriene formation via inhibition of 5-lipoxygenase (5-LO) by two boswellic acids, 11-keto-β-boswellic acid (KBA) and acetyl-11-keto-β-boswellic acid (AKBA). These two boswellic acids have also been chosen in the monograph of Indian frankincense in European Pharmacopoiea 6.0 as markers to ensure the quality of the air-dried gum resin exudate of B. serrata. Furthermore, several dietary supplements advertise the enriched content of KBA and AKBA. However, boswellic acids failed to inhibit leukotriene formation in human whole blood, and pharmacokinetic data revealed very low concentrations of AKBA and KBA in plasma, being far below the effective concentrations for bioactivity in vitro. Moreover, permeability studies suggest poor absorption of AKBA following oral administration. In view of these results, the previously assumed mode of action - that is, 5-LO inhibition - is questionable. On the other hand, 100-fold higher plasma concentrations have been determined for β-boswellic acid, which inhibits microsomal prostaglandin E synthase-1 and the serine protease cathepsin G. Thus, these two enzymes might be reasonable molecular targets related to the anti-inflammatory properties of BSE. In view of the results of clinical trials and the experimental data from in vitro studies of BSE, and the available pharmacokinetic and metabolic data on boswellic acids, this review presents different perspectives and gives a differentiated insight into the possible mechanisms of action of BSE in humans. It underlines BSE as a promising alternative to NSAIDs, which warrants investigation in further pharmacological studies and clinical trials.

Genetic deletion of mPGES-1 abolishes PGE2 production in murine dendritic cells and alters the cytokine profile, but does not affect maturation or migration

We undertook this study to determine the role of Microsomal PGE Synthase-1 (mPGES-1), and mPGES-1-generated Prostaglandin (PG) E2 on Dendritic Cell (DC) phenotype and function. Using mPGES-1 KnockOut (KO) mice, we generated bone marrow derived DCs and determined their eicosanoid production profile, cell surface marker expression, and cytokine production. We also assessed DC migratory and functional capacity in vivo. Compared to wild-type, mPGES-1 deficient DCs exhibited a markedly attenuated increase in PGE2 production upon LPS stimulation, and displayed preferential shunting towards PGD2 production. mPGES-1 KO DCs did not display deficiencies in maturation, migration or ability to sensitize T cells. However, mPGES-1 deficient DCs generated reduced amounts of the Th1 cytokine IL-12, which may in part be due to increased PGD2 rather than decreased PGE2. These findings provide useful information on the effects of inducible PGE2 on the innate immune system, and have important implications regarding potential consequences of pharmacologic mPGES-1 inhibition.

Understanding microscopic binding of human microsomal prostaglandin E synthase-1 (mPGES-1) trimer with substrate PGH2 and cofactor GSH: insights from computational alanine scanning and site-directed mutagenesis

Microsomal prostaglandin E synthase-1 (mPGES-1) is an essential enzyme involved in a variety of diseases and is the most promising target for the design of next-generation anti-inflammatory drugs. In order to establish a solid structural base, we recently developed a model of mPGES-1 trimer structure by using available crystal structures of both microsomal glutathione transferase-1 (MGST1) and ba3-cytochrome c oxidase as templates. The mPGES-1 trimer model has been used in the present study to examine the detailed binding of mPGES-1 trimer with substrate PGH(2) and cofactor GSH. Results obtained from the computational alanine scanning reveal the contribution of each residue at the protein-ligand interaction interface to the binding affinity, and the computational predictions are supported by the data obtained from the corresponding wet experimental tests. We have also compared our mPGES-1 trimer model with other available 3D models, including an alternative homology model and a low-resolution crystal structure, and found that our mPGES-1 trimer model based on the crystal structures of both MGST1 and ba3-cytochrome c oxidase is more reasonable than the other homology model of mPGES-1 trimer constructed by simply using a low-resolution crystal structure of MGST1 trimer alone as a template. The available low-resolution crystal structure of mPGES-1 trimer represents a closed conformation of the enzyme and thus is not suitable for studying mPGES-1 binding with ligands. Our mPGES-1 trimer model represents a reasonable open conformation of the enzyme and is therefore promising for studying mPGES-1 binding with ligands in future structure-based drug design targeting mPGES-1.

Prostaglandin E(2) synthase inhibition as a therapeutic target

BACKGROUND

Most NSAIDs function by inhibiting biosynthesis of PGE(2) by inhibition of COX-1 and/or COX-2. Since COX-1 has a protective function in the gastro-intestinal tract (GIT), non-selective inhibition of both cycloxy genases leads to moderate to severe gastro-intestinal intolerance. Attempts to identify selective inhibitors of COX-2, led to the identification of celecoxib and rofecoxib. However, long-term use of these drugs has serious adverse effects of sudden myocardial infarction and thrombosis. Drug-mediated imbalance in the levels of prostaglandin I(2) (PGI(2)) and thromboxane A(2) (TXA(2)) with a bias towards TXA(2) may be the primary reason for these events. This resulted in the drugs being withdrawn from the market, leaving a need for an effective and safe anti-inflammatory drug.

METHODS

Recently, the focus of research has shifted to enzymes downstream of COX in the prosta glandin biosynthetic pathway such as prostaglandin E(2) synthases. Microsomal prostaglandin E(2) synthase-1 (mPGES-1) specifically isomerizes PGH(2) to PGE(2), under inflammatory conditions. In this review, we examine the biology of mPGES-1 and its role in disease. Progress in designing molecules that can selectively inhibit mPGES-1 is reviewed.

CONCLUSION

mPGES-1 has the potential to be a target for anti-inflammatory therapy, devoid of adverse GIT and cardiac effects and warrants further investigation.

Prostaglandin E2 activates Rap1 via EP2/EP4 receptors and cAMP-signaling in rheumatoid synovial fibroblasts: involvement of Epac1 and PKA

The small GTPase Rap1 is implicated in a variety of cellar functions. In this study, we investigated the effect of prostaglandin E(2) (PGE(2)) on Rap1 activation in rheumatoid synovial fibroblasts (RSF). Rap1 was expressed in RSF, and GTP-bound active Rap1 (GTP-Rap1) was rapidly increased by PGE(2). The effect of PGE(2) was mimicked by an EP2 receptor agonist, an EP4 agonist and a cAMP-elevating agent forskolin with association to the increase of cAMP, but not by an EP1 or an EP3 agonist. RSF expressed the downstream signaling partners of cAMP, exchange protein directly activated by cAMP (Epac1) and protein kinase A (PKA). Both 8-pCPT-2-O-Me-cAMP (an Epac-specific cAMP analog) and 6-Bnz-cAMP (a PKA-specific cAMP analog) activated Rap1 in RSF. Activation of Rap1 by PGE(2) via cAMP-signaling may play an important role in the articular pathology of rheumatoid arthritis (RA).

Prostaglandins and sickness behavior: old story, new insights

Previous evidence has shown that prostaglandins play a key role in the development of sickness behavior observed during inflammatory states. In particular, prostaglandin E2 (PGE2) is produced in the brain by a variety of inflammatory signals such as endotoxins or cytokines. Its injection has been also shown to induce symptoms of sickness behavior. The role of cyclooxygenase enzymes (COX), the rate-limiting enzymes converting arachidonic acid into prostaglandins, in sickness behavior has been extensively studied, and it has been demonstrated that strategies aiming at inhibiting these enzymes limit anorexia, body weight loss and fever in animals with inflammatory diseases. However, inhibiting COX activity may lead to negative gastric or cardiovascular effects, since COX enzymes play a role in the synthesis of others prostanoids with various and sometimes contrasting properties. Recently, prostaglandin E synthases (PGES), which specifically catalyze the final step of PGE2 biosynthesis, were characterized. Among these enzymes, the microsomal prostaglandin E synthase-1 (mPGES-1) was of a particular interest since it was shown to be up-regulated by inflammatory signals in a variety of cell types. Moreover, mPGES-1 was shown to be crucial for correct immune-to-brain communication and induction of fever and anorexia by pro-inflammatory agents. This review takes stock of previous knowledge and recent advances in understanding the role of prostaglandins and of their specific synthesizing enzymes in the molecular mechanisms underlying sickness behavior. The review concludes with a short summary of key questions that remain to be addressed and points out therapeutic developments in this research field.

Synergistic up-regulation of prostaglandin E synthase expression in breast cancer cells by 17beta-estradiol and proinflammatory cytokines

Inflammatory mediators, such as cytokines and prostaglandins, play a fundamental role in estrogen-dependent breast cancer through their ability to up-regulate aromatase expression and subsequent local production of estrogens in the breast. To study the link between estrogens and inflammation further, we examined the regulation of prostaglandin E synthase (PTGES), a key enzyme in the production of prostaglandin E2. We found that 17beta-estradiol (E2) rapidly and robustly up-regulates PTGES mRNA and protein levels in estrogen receptor (ER)-positive breast cancer cells through ER recruitment to an essential estrogen response element located in the 5' flanking region of the PTGES gene. PTGES is also up-regulated by the proinflammatory cytokines TNFalpha or IL-1beta. Surprisingly, the combination of E2 and cytokines leads to a synergistic up-regulation of PTGES in an ER and nuclear factor-kappaB (NFkappaB)-dependent manner. This is in contrast to the mutual transrepression between ER and NFkappaB that has been well characterized in other cell types. Furthermore, we found enhanced recruitment of ERalpha as well as the NFkappaB family member, p65, to the PTGES estrogen response element by the combination of E2 and TNFalpha compared with either E2 or TNFalpha alone. The synergistic up-regulation of PTGES may result in enhanced prostaglandin E2 production, which in turn may further enhance aromatase expression and production of local estrogens. Our findings suggest that a finely tuned positive feedback mechanism between estrogens and inflammatory factors may exist in the breast and contribute to hormone-dependent breast cancer growth and progression.

Pulmonary and cardiorenal cyclooxygenase-1 (COX-1), -2 (COX-2), and microsomal prostaglandin E synthase-1 (mPGES-1) and -2 (mPGES-2) expression in a hypertension model

Hypertensive mice that express the human renin and angiotensinogen genes are used as a model for human hypertension because they develop hypertension secondary to increased renin-angiotensin system activity. Our study investigated the cellular localization and distribution of COX-1, COX-2, mPGES-1, and mPGES-2 in organ tissues from a mouse model of human hypertension. Male (n = 15) and female (n = 15) double transgenic mice (h-Ang 204/1 h-Ren 9) were used in the study. Lung, kidney, and heart tissues were obtained from mice at necropsy and fixed in 10% neutral buffered formalin followed by embedding in paraffin wax. Cut sections were stained immunohistochemically with antibodies to COX-1, COX-2, mPGES-1, and mPGES-2 and analyzed by light microscopy. Renal expression of COX-1 was the highest in the distal convoluted tubules, cortical collecting ducts, and medullary collecting ducts; while proximal convoluted tubules lacked COX-1 expression. Bronchial and bronchiolar epithelial cells, alveolar macrophages, and cardiac vascular endothelial cells also had strong COX-1 expression, with other renal, pulmonary, or cardiac microanatomic locations having mild-to-moderate expression. mPGES-2 expression was strong in the bronchial and bronchiolar epithelial cells, mild to moderate in various renal microanatomic locations, and absent in cardiac tissues. COX-2 expression was strong in the proximal and distal convoluted tubules, alveolar macrophages, and bronchial and bronchiolar epithelial cells. Marked mPGES-1 was present only in bronchial and bronchiolar epithelial cells; while mild-to-moderate expression was present in other pulmonary, renal, or cardiac microanatomic locations. Expression of these molecules was similar between males and females. Our work suggests that in hypertensive mice, there are (a) significant microanatomic variations in the pulmonary, renal, and cardiac distribution and cellular localization of COX-1, COX-2, mPGES-1, and mPGES-2, and (b) no differences in expression between genders.

Predominance of cyclooxygenase 1 over cyclooxygenase 2 in the generation of proinflammatory prostaglandins in autoantibody-driven K/BxN serum-transfer arthritis

OBJECTIVE

Prostaglandins (PGs) are found in high levels in the synovial fluid of patients with rheumatoid arthritis, and nonsteroidal blockade of these bioactive lipids plays a role in patient care. The aim of this study was to explore the relative contribution of cyclooxygenase (COX) isoforms and PG species in the autoantibody-driven K/BxN serum-transfer arthritis.

METHODS

The prostanoid content of arthritic ankles was assessed in ankle homogenates, and the importance of this pathway was confirmed with pharmacologic blockade. The presence of COX isoforms was assessed by Western blotting and their functional contribution was compared using COX-1-/- and COX-2-/- mice as well as isoform-specific inhibitors. The relative importance of PGE2 and PGI2 (prostacyclin) was determined using mice deficient in microsomal PGE synthase 1 (mPGES-1) and in the receptors for PGI2.

RESULTS

High levels of PGE2 and 6-keto-PGF1alpha (a stable metabolite of PGI2) were detected in arthritic joint tissues, correlating strongly with the intensity of synovitis. Pharmacologic inhibition of PG synthesis prevented arthritis and ameliorated active disease. While both COX isoforms were found in inflamed joint tissues, only COX-1 contributed substantially to clinical disease; COX-1-/- mice were fully resistant to disease, whereas COX-2-/- mice remained susceptible. These findings were confirmed by isoform-specific pharmacologic inhibition. Mice lacking mPGES-1 (and therefore PGE2) developed arthritis normally, whereas mice incapable of responding to PGI2 exhibited a significantly attenuated arthritis course, confirming a role of PGI2 in this arthritis model.

CONCLUSION

These findings challenge previous paradigms of distinct "housekeeping" versus inflammatory functions of the COX isoforms and highlight the potential pathogenic contribution of prostanoids synthesized via COX-1, in particular PGI2, to inflammatory arthritis.