Biological activities and mechanisms of action of PGJ2 and related compounds: an update

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

The omega-3 hydroxy fatty acid 7(S)-HDHA is a high-affinity PPARα ligand that regulates brain neuronal morphology

The nuclear receptor peroxisome proliferator-activated receptor alpha (PPARα) is emerging as an important target in the brain for the treatment or prevention of cognitive disorders. The identification of high-affinity ligands for brain PPARα may reveal the mechanisms underlying the synaptic effects of this receptor and facilitate drug development. Here, using an affinity purification-untargeted mass spectrometry (AP-UMS) approach, we identified an endogenous, selective PPARα ligand, 7(S)-hydroxy-docosahexaenoic acid [7(S)-HDHA]. Results from mass spectrometric detection of 7(S)-HDHA in mouse and rat brain tissues, time-resolved FRET analyses, and thermal shift assays collectively revealed that 7(S)-HDHA potently activated PPARα with an affinity greater than that of other ligands identified to date. We also found that 7(S)-HDHA activation of PPARα in cultured mouse cortical neurons stimulated neuronal growth and arborization, as well as the expression of genes associated with synaptic plasticity. The findings suggest that this DHA derivative supports and enhances neuronal synaptic capacity in the brain.

Platelet activating-factor acetylhydrolase II: A member of phospholipase A2 family that hydrolyzes oxidized phospholipids

Intracellular platelet activating-factor acetylhydrolase type II (PAF-AH II) is a 40-kDa monomeric enzyme. It was originally identified as an enzyme that hydrolyzes the acetyl group of PAF (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine). As a member of phospholipase A2 super family, PAF-AH II has broad substrate specificity. It can hydrolyze phospholipids with relatively short-length or oxidatively modified sn-2 chains which endows it with various functions such as protection against oxidative stress, transacetylase activity and producing lipid mediators. PAF-AH II has been proven to be involved in several diseases such as allergic diseases, oxidative stress-induced injury and ischemia injury, thus it has drawn more attention from researchers. In this paper, we outline an entire summary of PAF-AH II, including its structure, substrate specificity, activity assay, inhibitors and biological activities.

Molecular, chemical, and structural characterization of prostaglandin A2 as a novel agonist for Nur77

Nur77 is a transcription factor belonging to the NR4A subfamily of nuclear hormone receptors. Upon induction, Nur77 modulates the expression of its target genes and controls a variety of biological and pathophysiological processes. Prior research that revealed a structurally atypical ligand-binding domain (LBD) and failed to locate an endogenous ligand had led to a classification of Nur77 as an orphan receptor. However, several more recent studies indicate that small synthetic molecules and unsaturated fatty acids can bind to Nur77. Discovery of additional endogenous ligands will facilitate our understanding of the receptor's functions and regulatory mechanisms. Our data have identified prostaglandin A2 (PGA2), a cyclopentenone prostaglandin (PG), as such a ligand. Cyclopentenone PGs exert their biological effects primarily by forming protein adducts via the characteristic electrophilic β-carbon(s) located in their cyclopentenone rings. Our data show that PGA2 induces Nur77 transcriptional activity by forming a covalent adduct between its endocyclic β-carbon, C9, and Cys566 in the receptor's LBD. The importance of this endocyclic β-carbon was substantiated by the failure of PGs without such electrophilic properties to react with Nur77. Calculated chemical properties and data from reactive molecular dynamic simulations, intrinsic reaction co-ordinate modeling, and covalent molecular docking also corroborate the selectivity of PGA2's C9 β-carbon towards Nur77's Cys. In summary, our molecular, chemical, and structural characterization of the PGA2-Nur77 interaction provides the first evidence that PGA2 is an endogenous Nur77 agonist.

Identification and Molecular Characterization of Peroxisome Proliferator-Activated Receptor δ as a Novel Target for Covalent Modification by 15-Deoxy-Δ12,14-prostaglandin J2

PPARδ belongs to the peroxisome proliferator-activated receptor (PPAR) family of nuclear receptors. Upon activation by an agonist, PPARδ controls a variety of physiological processes via regulation of its target genes. 15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) is a cyclopentenone prostaglandin that features an electrophilic, α,β-unsaturated ketone (an enone) in the cyclopentenone ring. Many of 15d-PGJ2's biological effects result from covalent interaction between C9 and the thiol group of a catalytic cysteine (Cys) in target proteins. In this study, we investigated whether 15d-PGJ2 activates PPARδ by forming a covalent adduct. Our data show that 15d-PGJ2 activates PPARδ's transcriptional activity through formation of a covalent adduct between its endocyclic enone at C9 and Cys249 in the receptor's ligand-binding domain. As expected, no adduct formation was seen following a Cys-to-Ser mutation at residue 249 (C249S) of PPARδ or with a PGD2/PGJ2 analogue that lacks the electrophilic C9. Furthermore, the PPARδ C249S mutation weakened induction of the receptor's DNA binding activity by 15d-PGJ2, which highlights the biological significance of our findings. Calculated chemical properties as well as data from molecular orbital calculations, reactive molecular dynamics simulations, and intrinsic reaction coordinate modeling also supported the selectivity of 15d-PGJ2's C9 toward PPARδ's Cys thiol. In summary, our results provide the molecular, chemical, and structural basis of 15d-PGJ2-mediated PPARδ activation, designating 15d-PGJ2 as the first covalent PPARδ ligand to be identified.

The function of the oxylipin 12-oxophytodienoic acid in cell signaling, stress acclimation, and development

Forty years ago, 12-oxophytodienoic acid (12-OPDA) was reported as a prostaglandin (PG)-like metabolite of linolenic acid found in extracts of flaxseed. Since then, numerous studies have determined the role of 12-OPDA in regulating plant immunity, seed dormancy, and germination. This review summarizes our current knowledge of the regulation of 12-OPDA synthesis in the chloroplast and 12-OPDA-dependent signaling in gene expression and targeting protein functions. We describe the properties of OPDA that are linked to the activities of PGs, which are derived from arachidonic acid and act as tissue hormones in animals, including humans. The similarity of OPDA with bioactive PGs is particularly evident for the most-studied cyclopentenone, PG 15-dPGJ2. In addition to chemical approaches towards 12-OPDA synthesis, bio-organic synthesis strategies for 12-OPDA and analogous substances have recently been established. The resulting availability of OPDA will aid the identification of additional effector proteins, help in elucidating the mechanisms of OPDA sensing and transmission, and will foster the analysis of the physiological responses to OPDA in plants. There is a need to determine the compartmentation and transport of 12-OPDA and its conjugates, over long distances as well as short. It will be important to further study OPDA in animal and human cells, for example with respect to beneficial anti-inflammatory and anti-cancer activities.

Prevention of oxytosis-induced c-Raf down-regulation by (arylthio)cyclopentenone prostaglandins is neuroprotective

Prolonged exposure to high concentrations of glutamate leads to cell type specific glutathione depletion and resulting oxidative stress, known as oxytosis. As a result of glutathione depletion, accumulation of reactive oxygen species and Ca²⁺ influx are increased; however, the specific target of oxytosis has yet to be identified. In the present study, we focused on the effect of glutamate-induced oxidative stress on the extracellular-regulated protein kinase (ERK) pathway using the murine hippocampal HT22 cell line. Although the contribution of the ERK pathway to glutamate-induced oxytosis in HT22 cells is controversial, Western blot analysis revealed that glutamate caused down-regulation of mitogen-activated protein kinase kinase kinase (c-Raf) and a resulting decrease in the phosphorylation of c-Raf, as well as of mitogen-activated protein kinase kinase1/2 (MEK1/2) and ERK1/2, downstream components of the c-Raf/MEK/ERK pathway. Furthermore, neuroprotective (arylthio)cyclopentenone prostaglandins prevented glutamate-induced c-Raf down-regulation and consequently maintained the basal activity of c-Raf and its downstream signaling components. A pull-down assay using biotin-labeled cyclopentenone prostaglandins revealed that they preferentially bound to c-Raf relative to other signaling molecules of the ERK pathway, including Ras, MEK1/2, and ERK. These results suggest that neuroprotective (arylthio)cyclopentenone prostaglandins directly bind to c-Raf protein and protect cells from down-regulation of the c-Raf protein itself, resulting in neuroprotection against oxidative stress.

The plasma lipidome in acute myeloid leukemia at diagnosis in relation to clinical disease features

BACKGROUND

Early studies established that certain lipids were lower in acute myeloid leukemia (AML) cells than normal leukocytes. Because lipids are now known to play an important role in cell signaling and regulation of homeostasis, and are often perturbed in malignancies, we undertook a comprehensive lipidomic survey of plasma from AML patients at time of diagnosis and also healthy blood donors.

METHODS

Plasma lipid profiles were measured using three mass spectrometry platforms in 20 AML patients and 20 healthy blood donors. Data were collected on total cholesterol and fatty acids, fatty acid amides, glycerolipids, phospholipids, sphingolipids, cholesterol esters, coenzyme Q10 and eicosanoids.

RESULTS

We observed a depletion of plasma total fatty acids and cholesterol, but an increase in certain free fatty acids with the observed decline in sphingolipids, phosphocholines, triglycerides and cholesterol esters probably driven by enhanced fatty acid oxidation in AML cells. Arachidonic acid and precursors were elevated in AML, particularly in patients with high bone marrow (BM) or peripheral blasts and unfavorable prognostic risk. PGF2α was also elevated, in patients with low BM or peripheral blasts and with a favorable prognostic risk. A broad panoply of lipid classes is altered in AML plasma, pointing to disturbances of several lipid metabolic interconversions, in particular in relation to blast cell counts and prognostic risk.

CONCLUSIONS

These data indicate potential roles played by lipids in AML heterogeneity and disease outcome.

GENERAL SIGNIFICANCE

Enhanced catabolism of several lipid classes increases prognostic risk while plasma PGF2α may be a marker for reduced prognostic risk in AML.

Inhibitive effects of 15-deoxy-Δ(12),(14)-prostaglandin J2 on hepatoma-cell proliferation through reactive oxygen species-mediated apoptosis

OBJECTIVE

15-Deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) induces reactive oxygen species (ROS)-mediated apoptosis in many malignant cells, which has not been studied in hepatoma cells. In this study, we investigated whether 15d-PGJ2 induced apoptosis in hepatocellular carcinoma (HCC) associated with ROS.

MATERIALS AND METHODS

The LM3, SMMC-7721, and Huh-7 HCC cell lines were treated with 15d-PGJ2 (5-40 μM) for 24, 48, and 72 hours. Cholecystokinin 8 was used to detect the cytotoxicity of 15d-PGJ2. Flow cytometry, Hoechst staining, and Western blotting were used to analyze apoptosis. ROS were combined with the fluorescent probe dihydroethidium and then observed by fluorescence microscopy and flow cytometry. Activation of JNK and expression of Akt were detected by Western blotting.

RESULTS

15d-PGJ2 inhibited HCC cell proliferation and induced apoptosis in a dose- and time-dependent manner. Apoptosis was mainly induced via an intrinsic pathway and was ROS-dependent, and was alleviated by ROS scavengers. ROS induced JNK activation and Akt downregulation in HCC cells.

CONCLUSION

15d-PGJ2 induced ROS in HCC cell lines, and inhibition of cell growth and apoptosis were partly ROS-dependent.

Functional fluxolipidomics of polyunsaturated fatty acids and oxygenated metabolites in the blood vessel compartment

Synthesis of bioactive oxygenated metabolites of polyunsaturated fatty acids and their degradation or transformation products are made through multiple enzyme processes. The kinetics of the enzymes responsible for the different steps are known to be quite diverse, although not precisely determined. The location of the metabolites biosynthesis is diverse as well. Also, the biological effects of the primary and secondary products, and their biological life span are often completely different. Consequently, phenotypes of cells in response to these bioactive lipid mediators must then depend on their concentrations at a given time. This demands a fluxolipidomics approach that can be defined as a mediator lipidomics, with all measurements done as a function of time and biological compartments. This review points out what is known, even qualitatively, in the blood vascular compartment for arachidonic acid metabolites and number of other metabolites from polyunsaturated fatty acids of nutritional value. The functional consequences are especially taken into consideration.

Autocrine secretion of 15d-PGJ2 mediates simvastatin-induced apoptotic burst in human metastatic melanoma cells

BACKGROUND AND PURPOSE

Despite new therapeutic approaches, metastatic melanomas still have a poor prognosis. Statins reduce low-density lipoprotein cholesterol and exert anti-inflammatory and anti-proliferative actions. We have recently shown that simvastatin triggers an apoptotic burst in human metastatic melanoma cells by the synthesis of an autocrine factor.

EXPERIMENTAL APPROACH

The current in vitro study was performed in human metastatic melanoma cell lines (A375, 518a2) and primary human melanocytes and melanoma cells. The secretome of simvastatin-stressed cells was analysed with two-dimensional difference gel electrophoresis and MS. The signalling pathways involved were analysed at the protein and mRNA level using pharmacological approaches and siRNA technology.

KEY RESULTS

Simvastatin was shown to activate a stress cascade, leading to the synthesis of 15-deoxy-12,14-PGJ2 (15d-PGJ2 ), in a p38- and COX-2-dependent manner. Significant concentrations of 15d-PGJ2 were reached in the medium of melanoma cells, which were sufficient to activate caspase 8 and the mitochondrial pathway of apoptosis. Inhibition of lipocalin-type PGD synthase, a key enzyme for 15d-PGJ2 synthesis, abolished the apoptotic effect of simvastatin. Moreover, 15d-PGJ2 was shown to bind to the fatty acid-binding protein 5 (FABP5), which was up-regulated and predominantly detected in the secretome of simvastatin-stressed cells. Knockdown of FABP5 abolished simvastatin-induced activation of PPAR-γ and amplified the apoptotic response.

CONCLUSIONS AND IMPLICATIONS

We characterized simvastatin-induced activation of the 15d-PGJ2 /FABP5 signalling cascades, which triggered an apoptotic burst in melanoma cells but did not affect primary human melanocytes. These data support the rationale for the pharmacological targeting of 15d-PGJ2 in metastatic melanoma.

15-Deoxy-Δ¹²,¹⁴-prostaglandin J₂ as an electrophilic mediator

Lipid-derived electrophilic molecules are endogenously generated and are causally involved in many pathophysiological effects. Prostaglandin D2, a major cyclooxygenase product in a variety of tissues and cells, readily undergoes dehydration to yield the J-series PGs such as 15-deoxy-Δ(12,14)-PGJ2 (15d-PGJ2). Because of the electrophilic α,β-unsaturated ketone moiety present in its cyclopentenone ring, 15d-PGJ2 acts as an endogenous electrophile. 15d-PGJ2 can covalently react via the Michael addition reaction with critical cellular nucleophiles, such as the free cysteine residues of proteins that play a key role in the regulation of the intracellular signaling pathways. Covalent modification of cellular proteins by 15d-PGJ2 may be one of the most important mechanisms by which 15d-PGJ2 induces many biological responses involved in the pathophysiological effects associated with inflammation. This current review is intended to provide a comprehensive summary of 15d-PGJ2 as an endogenous electrophilic mediator of biological activities.

Eicosanoids and adipokines in breast cancer: from molecular mechanisms to clinical considerations

Chronic inflammation is one of the foremost risk factors for different types of malignancies, including breast cancer. Additional risk factors of this pathology in postmenopausal women are weight gain, obesity, estrogen secretion, and an imbalance in the production of adipokines, such as leptin and adiponectin. Various signaling products of transcription factor, nuclear factor-kappaB, in particular inflammatory eicosanoids, reactive oxygen species (ROS), and cytokines, are thought to be involved in chronic inflammation-induced cancer. Together, these key components have an influence on inflammatory reactions in malignant tissue damage when their levels are deregulated endogenously. Prostaglandins (PGs) are well recognized in inflammation and cancer, and they are solely biosynthesized through cyclooxygenases (COXs) from arachidonic acid. Concurrently, ROS give rise to bioactive isoprostanes from arachidonic acid precursors that are also involved in acute and chronic inflammation, but their specific characteristics in breast cancer are less demonstrated. Higher aromatase activity, a cytochrome P-450 enzyme, is intimately connected to tumor growth in the breast through estrogen synthesis, and is interrelated to COXs that catalyze the formation of both inflammatory and anti-inflammatory PGs such as PGE(2), PGF(2α), PGD(2), and PGJ(2) synchronously under the influence of specific mediators and downstream enzymes. Some of the latter compounds upsurge the intracellular cyclic adenosine monophosphate concentration and appear to be associated with estrogen synthesis. This review discusses the role of COX- and ROS-catalyzed eicosanoids and adipokines in breast cancer, and therefore ranges from their molecular mechanisms to clinical aspects to understand the impact of inflammation.

Neuroprotective cyclopentenone prostaglandins up-regulate neurotrophic factors in C6 glioma cells

In a previous study, we developed newly synthesized arylthio derivatives of cyclopentenone prostaglandins (GIF-0642, GIF-0643, GIF-0644, GIF-0745 and GIF-0747), which are neuroprotective against both manganese toxicity in PC12 cells and glutamate toxicity in HT22 cells. In the present study, we showed that these compounds and their lead compound, NEPP11, are potent inducers of glial cell line-derived neurotrophic factor (GDNF) expression in C6 glioma cells and primary astrocytes. These neuroprotective cyclopentenone prostaglandins also induced the gene expression of nerve growth factor and, to a lesser extent, brain-derived neurotrophic factor. The induction of GDNF mRNA was transcription-dependent, and the overexpression of dominant-negative Nrf2 attenuated the ability of the (arylthio)cyclopentenone prostaglandins to stimulate GDNF gene expression. These results suggest that (arylthio)cyclopentenone prostaglandins increase GDNF gene expression partly via the Keap1/Nrf2 pathway. A growing number of reports demonstrate the importance of increasing the amounts of neurotrophic factors, especially GDNF, in neuropathological states. Although the precise mechanisms by which the GIF compounds inhibit cell death are under investigation, an increase in neurotrophic factors may contribute to the diverse pharmacological properties of (arylthio)cyclopentenone prostaglandins in vivo and will make them potentially valuable in the treatment of neurodegenerative disorders.

Inflammatory bowel disease and pregnancy: overlapping pathways

Several studies have reported on the association between inflammatory bowel disease (IBD) and adverse pregnancy outcomes, such as preterm birth. The exact mechanisms of action are unclear; however, several pathways and processes are involved in both IBD and pregnancy that may help explain this. In this review, we discuss the immune system's T helper cells and human leukocyte antigens, inflammation, its function, and the role of Toll-like receptors (TLRs), NOD-like receptors (NLRs), and prostaglandins in the inflammatory response. For each of these topics, we consider their involvement in IBD and pregnancy, and we speculate as to how they can lead to preterm birth. Finally, we review briefly corticosteroids, biologic therapies, and immunosuppressants for the treatment of IBD, as well as their safety in use during pregnancy, with special focus on preterm birth.

PPARgamma in Neuroblastoma

Neuroblastoma (NB) is the most common extracranial tumor in children and accounts for around 15% of all paediatric oncology deaths. The treatment of NB includes surgery, chemotherapy, and radiotherapy. Unfortunately, most children with NB present with advanced disease, and more than 60% of patients with high-risk features will have a poor prognosis despite intensive therapy. Agonists of the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) have been shown to have pleiotropic effects, including antineoplastic effects. The studies that addressed the role and the possible mechanism(s) of action of PPARgamma in NB cells are reviewed.

Regulation of Lymphocyte Function by PPARgamma: Relevance to Thyroid Eye Disease-Related Inflammation

Thyroid eye disease (TED) is an autoimmune condition in which intense inflammation leads to orbital tissue remodeling, including the accumulation of extracellular macromolecules and fat. Disease progression depends upon interactions between lymphocytes and orbital fibroblasts. These cells engage in a cycle of reciprocal activation which produces the tissue characteristics of TED. Peroxisome proliferator-activated receptor-gamma (PPARgamma) may play divergent roles in this process, both attenuating and promoting disease progression. PPARgamma has anti-inflammatory activity, suggesting that it could interrupt intercellular communication. However, PPARgamma activation is also critical to adipogenesis, making it a potential culprit in the pathological fat accumulation associated with TED. This review explores the role of PPARgamma in TED, as it pertains to crosstalk between lymphocytes and fibroblasts and the development of therapeutics targeting cell-cell interactions mediated through this signaling pathway.

Role of peroxisome proliferator-activated receptor gamma and its ligands in the treatment of hematological malignancies

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a multifunctional transcription factor with important regulatory roles in inflammation, cellular growth, differentiation, and apoptosis. PPARgamma is expressed in a variety of immune cells as well as in numerous leukemias and lymphomas. Here, we review recent studies that provide new insights into the mechanisms by which PPARgamma ligands influence hematological malignant cell growth, differentiation, and survival. Understanding the diverse properties of PPARgamma ligands is crucial for the development of new therapeutic approaches for hematological malignancies.

Peroxisome proliferator-activated receptor gamma ligands enhance human B cell antibody production and differentiation

Protective humoral immune responses critically depend on the optimal differentiation of B cells into Ab-secreting cells. Because of the important role of Abs in fighting infections and in successful vaccination, it is imperative to identify mediators that control B cell differentiation. Activation of B cells through TLR9 by CpG-DNA induces plasma cell differentiation and Ab production. Herein, we examined the role of the peroxisome proliferator-activated receptor (PPAR)gamma/RXRalpha pathway on human B cell differentiation. We demonstrated that activated B cells up-regulate their expression of PPARgamma. We also show that nanomolar levels of natural (15-deoxy-Delta(12,14)-prostaglandin J(2)) or synthetic (rosiglitazone) PPARgamma ligands enhanced B cell proliferation and significantly stimulated plasma cell differentiation and Ab production. Moreover, the addition of GW9662, a specific PPARgamma antagonist, abolished these effects. Retinoid X receptor (RXR) is the binding partner for PPARgamma and is required to produce an active transcriptional complex. The simultaneous addition of nanomolar concentrations of the RXRalpha ligand (9-cis-retinoic acid) and PPARgamma ligands to CpG-activated B cells resulted in additive effects on B cell proliferation, plasma cell differentiation, and Ab production. Furthermore, PPARgamma ligands alone or combined with 9-cis-retinoic acid enhanced CpG-induced expression of Cox-2 and the plasma cell transcription factor BLIMP-1. Induction of these important regulators of B cell differentiation provides a possible mechanism for the B cell-enhancing effects of PPARgamma ligands. These new findings indicate that low doses of PPARgamma/RXRalpha ligands could be used as a new type of adjuvant to stimulate Ab production.

15d-PGJ2 induces apoptosis by reactive oxygen species-mediated inactivation of Akt in leukemia and colorectal cancer cells and shows in vivo antitumor activity

PURPOSE

Recent studies have shown that 15-deoxy-Delta(12, 14)-prostaglandin J(2) (15d-PGJ(2)), a natural ligand for peroxisome proliferator-activated receptor-gamma (PPARgamma), inhibits cell proliferation and induces apoptosis. The specific molecular mechanisms underlying this effect remain to be elucidated. We examined whether 15d-PGJ(2) has antitumor activity in vitro and in vivo, and investigated the underlying mechanism.

EXPERIMENTAL DESIGN

We examined 15d-PGJ(2)-induced apoptosis in human leukemia cells in the context of mitochondrial injury, oxidative damage, and signaling pathway disturbances. In addition, we investigated the antitumor effect of 15d-PGJ(2) in a mouse CT-26 s.c. tumor model and HL-60 leukemia xenograft model.

RESULTS

15d-PGJ(2) induced apoptosis in leukemia and colorectal cancer cells in a dose-dependent manner and led to generation of reactive oxygen species (ROS) through mitochondria and NADPH oxidase activation, activation of JNK, and inactivation of Akt, a serine/threonine-specific protein kinase. Constitutive activation of Akt for an engineered myristoylated protein prevented 15d-PGJ(2)-mediated apoptosis but not ROS generation. Collectively, these findings suggest a hierarchical model of apoptosis induced by 15d-PGJ(2) in human leukemia cells: oxidative injury represents a primary event resulting in Akt inactivation, which in turn leads to mitochondrial injury and apoptosis. Moreover, 15d-PGJ(2) markedly reduced growth of mouse CT-26 s.c. tumors and HL-60 xenograft tumors and down-regulated p-Akt and Akt expression in vivo.

CONCLUSIONS

These results suggest that Akt inactivation through ROS production may contribute to 15d-PGJ(2)-induced apoptosis in leukemia and colorectal cancer cell lines and that 15d-PGJ(2) may have therapeutic relevance in the treatment of human leukemia and colorectal cancer.

Neuroprotective effects of (arylthio)cyclopentenone derivatives on manganese-induced apoptosis in PC12 cells

Parkinson's disease is characterized by degeneration of dopaminergic neurones in the substantia nigra. Chronic manganese poisoning shares many features of Parkinson's disease, and also induces extrapyramidal syndromes that resemble those of Parkinson's disease due to dopamine depletion in the central nervous system. This study was undertaken to develop novel neuroprotective drugs via the identification of compounds that inhibit manganese-induced apoptosis. Here, we report that (arylthio)cyclopentenone derivatives, which are synthetic analogs of cyclopentenone prostaglandins, prevent manganese-induced apoptosis in PC12 cells. A highly sensitive assay of caspase-3/7 activity was used for screening newly synthesized prostaglandin analogs. The results showed that some cyclopentenone derivatives (GIF-0642, GIF-0643, GIF-0644, GIF-0745, and GIF-0747) inhibit manganese-induced caspase-3/7 activation in a concentration-dependent manner. Effective compounds all have an arylthio group, indicating that this structure plays an important role in the anti-apoptotic effects of (arylthio)cyclopentenone derivatives. The anti-apoptotic effects of these compounds were confirmed by verifying their ability to inhibit the DNA fragmentation and caspase-9 activation induced by manganese. Furthermore, GIF-0747 prevented manganese-induced cytochrome c release from mitochondria. These results suggest that (arylthio)cyclopentenone derivatives may be good candidates for treating neurodegenerative diseases.

15-deoxy-Delta12,14 prostaglandin J2-induced heme oxygenase-1 in megakaryocytes regulates thrombopoiesis

BACKGROUND

Platelet production is an intricate process that is poorly understood. Recently, we demonstrated that the natural peroxisome proliferator-activated receptor gamma (PPARgamma) ligand, 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)), augments platelet numbers by increasing platelet release from megakaryocytes through the induction of reactive oxygen species (ROS). 15d-PGJ(2) can exert effects independent of PPARgamma, such as increasing oxidative stress. Heme oxygenase-1 (HO-1) is a potent antioxidant and may influence platelet production.

OBJECTIVES

To further investigate the influence of 15d-PGJ(2) on megakaryocytes and to understand whether HO-1 plays a role in platelet production.

METHODS

Meg-01 cells (a primary megakaryoblastic cell line) and primary human megakaryocytes derived from cord blood were used to examine the effects of 15d-PGJ(2) on HO-1 expression in megakaryocytes and their daughter platelets. The role of HO-1 activity in thrombopoiesis was studied using established in vitro models of platelet production.

RESULTS AND CONCLUSIONS

15d-PGJ(2) potently induced HO-1 protein expression in Meg-01 cells and primary human megakaryocytes. The platelets produced from these megakaryocytes also expressed elevated levels of HO-1. 15d-PGJ(2)-induced HO-1 was independent of PPARgamma, but could be replicated using other electrophilic prostaglandins, suggesting that the electrophilic properties of 15d-PGJ(2) were important for HO-1 induction. Interestingly, inhibiting HO-1 activity enhanced ROS generation and augmented 15d-PGJ(2)-induced platelet production, which could be attenuated by antioxidants. These new data reveal that HO-1 negatively regulates thrombopoiesis by inhibiting ROS.

[Pathophysiological relevance of peroxisome proliferators activated receptors (PPAR) to joint diseases - the pro and con of agonists]

Peroxisome proliferators activated receptors (PPAR) are ligand-inducible nuclear transacting factors comprising three subtypes, PPARalpha, PPARbeta/delta and PPARgamma, which play a key role in lipids and glucose homeostasis. All PPAR subtypes have been identified in joint or inflammatory cells and their activation resulted in a transcriptional repression of pro-inflammatory cytokines (IL-1, TNFalpha), early inflammatory genes (NOS(2), COX-2, mPGES-1) or matrix metalloproteases (MMP-1, MMP-13), at least for the gamma subtype. PPAR full agonists were also shown to stimulate IL-1 receptor antagonist (IL-1Ra) production by cytokine-stimulated articular cells in a subtype-dependent manner. These anti-inflammatory and anti-catabolic properties were confirmed in animal models of joint diseases where PPAR agonists reduced synovial inflammation while preventing cartilage destruction or inflammatory bone loss, although many effects required much higher doses than needed to restore insulin sensitivity or to lower circulating lipid levels. However, these promising effects of PPAR full agonists were hampered by their ability to reduce the growth factor-dependent synthesis of extracellular matrix components or to induce chondrocyte apoptosis, by the possible contribution of immunosuppressive properties to their anti-arthritic effects, by the increased adipocyte differentiation secondary to prolonged stimulation of PPARgamma, and by a variable contribution of PPAR subtypes depending on the system. Clinical data are scarce in rheumatoid arthritis (RA) patients whereas thousands of patients worldwilde, treated with PPAR agonists for type 2 diabetes or dyslipidemia, are paradoxically prone to suffer from osteoarthritis (OA). Whereas high dosage of full agonists may expose RA patients to cardiovascular adverse effects, the proof of concept that PPAR agonists have therapeutical relevance to OA may benefit from an epidemiological follow-up of joint lesions in diabetic or hyperlipidemic patients treated for long periods of time with glitazones or fibrates. Additionally, cellular and animal studies are required to assess whether partial agonists of PPAR (SPPARMs) may preserve therapeutical properties with potentially less safety concern.

15-deoxy-delta12,14-PGJ2 enhances platelet production from megakaryocytes

Thrombocytopenia is a critical problem that occurs in many hematologic diseases, as well as after cancer therapy and radiation exposure. Platelet transfusion is the most commonly used therapy but has limitations of alloimmunization, availability, and expense. Thus, the development of safe, small, molecules to enhance platelet production would be advantageous for the treatment of thrombocytopenia. Herein, we report that an important lipid mediator and a peroxisome proliferator-activated receptor gamma (PPARgamma) ligand called 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)), increases Meg-01 maturation and platelet production. 15d-PGJ(2) also promotes platelet formation from culture-derived mouse and human megakaryocytes and accelerates platelet recovery after in vivo radiation-induced bone marrow injury. Interestingly, the platelet-enhancing effects of 15d-PGJ(2) in Meg-01 cells are independent of PPARgamma, but dependent on reactive oxygen species (ROS) accumulation; treatment with antioxidants such as glutathione ethyl ester (GSH-EE); or N-acetylcysteine (NAC) attenuate 15d-PGJ(2)-induced platelet production. Collectively, these data support the concept that megakaryocyte redox status plays an important role in platelet generation and that small electrophilic molecules may have clinical efficacy for improving platelet numbers in thrombocytopenic patients.

15-deoxy-Delta(12,14)-prostaglandin J2 induces vascular endothelial cell apoptosis through the sequential activation of MAPKS and p53

15-Deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) is a potent anti-angiogenic factor and induces endothelial cell apoptosis, although the mechanism remains unclear. In this study, 15d-PGJ(2) was found to increase p53 levels of the human umbilical vein endothelial cells by stabilizing p53. Both 15d-PGJ(2)-induced apoptosis and the induction of p21(Waf1) and Bax can be abolished by p53 small interfering RNA but not by peroxisome proliferator-activated receptor gamma inhibitors. Moreover, 15d-PGJ(2) activated JNK and p38 MAPK while inducing p53 phosphorylation at sites responsible for p53 activity. JNK inhibitor (SP600125) or p38 MAPK inhibitor (SB203580) pretreatment attenuated 15d-PGJ(2)-mediated apoptosis and suppressed the p21(Waf1) and Bax expressions without affecting p53 protein accumulation. Pretreatment with SP600125 partially prevented the phosphorylation of p53 at serines 33 and 392 induced by 15d-PGJ(2). 15d-PGJ(2) was also found to induce reactive oxygen species generation and partially blocked nuclear factor-kappaB activity. Pretreatment with antioxidant N-acetylcysteine prevented the p53 accumulation, the phosphorylations of JNK and p38 MAPK, the inhibition of NF-kappaB activity, as well as the apoptosis induced by 15d-PGJ(2). Using a mouse model of corneal neovascularization, it was demonstrated in vivo that 15d-PGJ(2) induced reactive oxygen species generation, activated JNK and p38 MAPK, induced p53 accumulation/phosphorylation, and induced vascular endothelial cell apoptosis, which could be abolished by N-acetylcysteine, SP600125, SB203580, or a virus-derived amphipathic peptides-based p53 small interfering RNA. This is the first study that 15d-PGJ(2) induces vascular endothelial cell apoptosis through the signaling of JNK and p38 MAPK-mediated p53 activation both in vitro and in vivo, further establishing the potential of 15d-PGJ(2) as an anti-angiogenesis agent.

15-Deoxy-Delta(12,14)-prostaglandin J2: an electrophilic trigger of cellular responses

Electrophilic molecules are endogenously generated and are causally involved in many pathophysiological effects. Prostaglandin D (20 (PGD (2)), a major cyclooxygenase product in a variety of tissues, readily undergoes dehydration to yield the cyclopentenone-type PGs of the J (2)-series such as 15-deoxy-Delta (12,14)-PGJ (2) (15d-PGJ (2)). 15d-PGJ (2) is an electrophile, which can covalently react via the Michael addition reaction with nucleophiles, such as the free sulfhydryls of glutathione and cysteine residues in cellular proteins that play an important role in the control of the redox cell-signaling pathways. Covalent binding of 15d-PGJ (2) to cellular proteins may be one of the mechanisms by which 15d-PGJ (2) induces a cellular response involved in most of the pathophysiological effects associated with inflammation. In the present perspective, we provide a comprehensive summary of 15d-PGJ (2) as an electrophilic mediator of cellular responses.

Conjugated linoleic acids can change phagocytosis of human monocytes/macrophages by reduction in Cox-2 expression

Prostaglandin E2 produced endogenously (by cyclooxygenases) can regulate macrophage phagocytosis. Cyclooxygenase activity reduction (mainly through inhibition of inducible Cox-2) can induce PGE2 synthesis depression and can activate the phagocytosis process. There are no reports in the literature explaining whether conjugated linoleic acid dienes (trans-10, cis-12 CLA and cis-9, trans-11 CLA) modify the phagocytic activity of human macrophages. For the purpose of this study, monocytes were isolated from venous blood, incubated for 7 days with 30 microM CLAs, and then (in some experiments) LPS (1 microg/mL) was added to the medium. Subsequently, monocyte/macrophage phagocytosis, NF-kappaB transcription factor activity, Cox-2 and PPARgamma mRNA expression (and the amounts of Cox-2 and PPARgamma proteins) and PGE2 synthesis were determined. Both CLA isomers increased macrophage phagocytosis through inhibition of Cox-2 expression (might by inactivation the NF-kappaB pathway). The inhibition of mRNA Cox-2 expression contributed (particularly with respect to trans-10, cis-12 CLA) to a decrease in protein Cox-2 synthesis and to reduction of prostaglandin E2 content in the cell. The inhibition of PGE2 synthesis (by CLA treatment) enhanced the phagocytosis process in macrophages.

15d-PGJ2 stimulates HO-1 expression through p38 MAP kinase and Nrf-2 pathway in rat vascular smooth muscle cells

15d-PGJ(2), a potent endogenous ligand for peroxisome proliferators activated receptor-gamma, is a cyclopentenone-type prostaglandin produced by many different types of cells. Pertinent to its effect on vascular smooth muscle cell (VSMC), antiproliferative effects have been most frequently reported. In the present study, we investigated the effect of 15d-PGJ(2) on HO-1 expression that has been reported to inhibit VSMC proliferation. According to our data, 15d-PGJ(2) significantly induced ROS/NO production and HO-1 expression in rVSMCs. We also observed 15d-PGJ(2)-induced translocation of Nrf-2. In addition, ROS scavenger pretreatment suppressed 15d-PGJ(2)-induced HO-1 expression while PPARgamma antagonist did not, suggesting nuclear translocation of Nrf-2 and subsequent HO-1 expression was ROS dependent rather than PPARgamma dependent. Furthermore, an inhibitor of p38 MAPK abolished 15d-PGJ(2)-induced HO-1 expression. These data suggest that 15d-PGJ(2)-induced up-regulation of HO-1 is independent of PPARgamma but dependent of ROS and p38 MAPK pathway. The present study reports for the first time that 15d-PGJ(2) induces HO-1 expression possibly using Nrf-2 pathway as a response to ROS in VSMCs.

Simultaneous quantification of seven prostanoids using liquid chromatography/tandem mass spectrometry: the effects of arachidonic acid on prostanoid production in mouse bone marrow-derived mast cells

We have developed a method for the simultaneous estimation of the levels of the prostanoids 6-keto prostaglandin (PG) Flalpha, PGB2, PGD2, PGE2, PGF2(alpha), PGJ2, and thromboxane (TX) B2 in blood- or serum-containing medium using liquid chromatography-tandem mass spectrometry. These prostanoids and their deuterium derivatives, which were used as internal standards, were subjected to solid-phase extraction using Empore C18 HD disk cartridges and analyzed in the selected reaction-monitoring mode. A linear response curve starting at 10 pg of prostanoid/tube was observed for each prostanoid. The accuracy of the method was demonstrated with samples containing known amounts of the prostanoids. Furthermore, we used this method to analyze the prostanoids produced in mouse bone marrow-derived mast cells stimulated with arachidonic acid, which resulted in the production of PGD2, PGE2, PGF2alpha, and TXB2. The results suggest that this simultaneous quantification method is useful for the analysis of the production of biomedically important prostanoids.

Sequential induction of pro- and anti-inflammatory prostaglandins and peroxisome proliferators-activated receptor-gamma during normal wound healing: a time course study

Lipid mediators generated from metabolism of arachidonic acid play a crucial role in the initiating and resolution of acute inflammation by shifting from pro-inflammatory prostaglandin (PG) E2 to anti-inflammatory PGD2 and its metabolites. The changes in PG levels over time during the normal wound-repair process have not, however, been reported. We determined the temporal expression of PG and their biosynthetic enzymes using the full thickness incisional model of normal wound healing in mice. We demonstrate that during normal wound repair, there is a shift in the metabolism of arachidonate from PGE2 during the acute inflammatory phase to PGD2 during the repair phase. This shift is mediated by temporal changes in the expression of cyclooxygenases (COX) and microsomal PGES (mPGES)-1. Inducible COX (COX-2) expression is sustained throughout the initiation and repair process, but mPGES-1 is increased only during the acute inflammatory phase and its disappearance coincides with increased PGD2. PGD2 and its degradation products are known to mediate their anti-inflammatory effects by binding to peroxisome proliferators-activated receptor gamma (PPARgamma). In this study, we show that PPARgamma is upregulated during the resolution phase of wound repair concomitant with the shift to PGD2, and may be responsible for initiating endogenous mechanism resulting in healing/resolution.

Activated human T lymphocytes express cyclooxygenase-2 and produce proadipogenic prostaglandins that drive human orbital fibroblast differentiation to adipocytes

The differentiation of preadipocyte fibroblasts to adipocytes is a crucial process to many disease states including obesity, cardiovascular, and autoimmune diseases. In Graves' disease, the orbit of the eye can become severely inflamed and infiltrated with T lymphocytes as part of the autoimmune process. The orbital fibroblasts convert to fat-like cells causing the eye to protrude, which is disfiguring and can lead to blindness. Recently, the transcription factor peroxisome proliferator activated receptor (PPAR)-gamma and its natural (15d-PGJ2) and synthetic (thiazolidinedione-type) PPAR-gamma agonists have been shown to be crucial to the in vitro differentiation of preadipocyte fibroblasts to adipocytes. We show herein several novel findings. First, that activated T lymphocytes from Graves' patients drive the differentiation of PPAR-gamma-expressing orbital fibroblasts to adipocytes. Second, this adipogenic differentiation is blocked by nonselective small molecule cyclooxygenase (Cox)-1/Cox-2 inhibitors and by Cox-2 selective inhibitors. Third, activated, but not naïve, human T cells highly express Cox-2 and synthesize prostaglandin D2 and related prostaglandins that are PPAR-gamma ligands. These provocative new findings provide evidence for how activated T lymphocytes, through production of PPAR-gamma ligands, profoundly influence human fibroblast differentiation to adipocytes. They also suggest the possibility that, in addition to the orbit, T lymphocytes influence the deposition of fat in other tissues.

The NR4A nuclear receptor family in eosinophils

It is well-known that many members of the family of nuclear receptors have been implicated in human diseases, and metabolic disorders in particular. The NR4A nuclear receptor family consists of three members, Nur77, Nurr1, and NOR1. All of these are orphan receptors, and Nur77 and NOR1 exert possible pathological roles in immune diseases through the modulation of leukocyte functions. CD30 stimulation, which induces eosinophil-specific apoptosis, markedly enhances expression of Nur77 and NOR1 in eosinophils. This suggests the possibility of pharmacological modulation of Nur77- or NOR1-specific apoptotic pathways via receptor-dependent transactivation. In this review, we discuss treatment of allergic diseases by low molecular weight compounds acting through the NR4A receptor family to cause eosinophil apoptosis. NR4A nuclear receptor genes were selected following comprehensive analysis of differentially expressed genes in eosinophils of atopic dermatitis patients compared with healthy volunteers.

The Peroxisome Proliferator-Activated Receptor γ (PPARγ) Ligands 15-Deoxy-Δ12,14-Prostaglandin J2 and Ciglitazone Induce Human B Lymphocyte and B Cell Lymphoma Apoptosis by PPARγ-Independent Mechanisms

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a transcription factor important for adipogenesis and more recently has been shown to be an anticancer target. PPARgamma ligands, including the endogenous ligand 15-deoxy-Delta12,14-PGJ2 (15d-PGJ2) and synthetic ligands like ciglitazone and troglitazone, all induce apoptosis in normal and malignant human B lymphocytes, but the dependency of PPARgamma for apoptosis induction is unknown. In this study, we used a PPARgamma dominant-negative approach and a small molecule irreversible PPARgamma antagonist and found that these inhibitors prevented PPARgamma activation but did not prevent B cell apoptosis induced by 15d-PGJ2 or ciglitazone. In addition, a PPARgamma agonist that is a structural analog of 15d-PGJ2, and lacks the electrophilic carbon of the 15d-PGJ2 cyclopentenone ring, activated PPARgamma but did not kill B lymphocytes, further supporting a non-PPARgamma-mediated mechanism. To further investigate the apoptotic mechanism, the effects of 15d-PGJ2 and ciglitazone on reactive oxygen species were investigated. 15d-PGJ2, but not ciglitazone, potently induced reactive oxygen species in B lymphocytes, implicating the reactive nature of the 15d-PGJ2 structure in the apoptosis mechanism. In addition, 15d-PGJ2 caused an almost complete depletion of intracellular glutathione. Moreover, incubation with glutathione reduced ethyl ester, an antioxidant, prevented apoptosis induced by 15d-PGJ2, but not by ciglitazone. These findings indicate that the expression of PPARgamma may not be predictive of whether a normal or malignant B lineage cell is sensitive to PPARgamma agonists. Furthermore, these new findings support continued investigation into the use of PPARgamma agonists as agents to attenuate normal B cell responses and as anti-B cell lymphoma agents.

Prostaglandin-induced programmed cell death in Trypanosoma brucei involves oxidative stress

Recently, we reported the induction of a programmed cell death (PCD) in bloodstream forms of Trypanosoma brucei by prostaglandin D(2) (PGD(2)). As this prostanoid is readily metabolized in the presence of albumin, we were prompted to investigate if PGD(2) metabolites rather than PGD(2) itself are responsible for the observed PCD. In fact, J series metabolites, especially PGJ(2) and Delta(12)PGJ(2), were able to induce PCD more efficiently than PGD(2). However, the stable PGD(2) analog 17phenyl-trinor-PGD(2) led to the same phenotype as the natural PGD(2), indicating that the latter induces PCD as well. Interestingly, the intracellular reactive oxygen species (ROS) level increased significantly under J series metabolites treatment and, incubation with N-acetyl-L-cysteine or glutathione reduced ROS production and cell death significantly. We conclude that PGJ(2) and Delta(12)PGJ(2) formation within the serum represents a mechanism to amplify PGD(2)-induced PCD in trypanosomes via ROS production.

Solid-Phase Synthesis and Biological Activity of a Combinatorial Cross-Conjugated Dienone Library

The solid-phase synthesis of a combinatorial cross-conjugated dienone library based on the structure of clavulones and their biological activity are reported. Clavulones are a family of marine prostanoids, and are composed of a cross-conjugated dienone system bearing two alkyl side-chains. The cross-conjugated dienone system irreversibly reacted with two nucleophiles. Our strategy for the solid-phase synthesis of the cross-conjugated dienones involves the Sonogashira-coupling reaction of a solid-supported cyclopentenone 10 bearing an acetylene group, followed by aldol condensation with aldehydes. The diphenyl derivative 7 aA was prepared from the solid-supported cyclopentenone 10 in 56% total yield. Combinatorial synthesis of a small library using twelve halides and eight aldehydes resulted in the production of 74 desired compounds from 98 candidates, and were detected by their mass spectra. Antiproliferative effects of the crude compounds against HeLaS3 cells showed that eleven samples showed strong antitumor activity (IC50<0.05 microM). Further biological examination of four purified compounds by using five tumor cell lines (A549, HeLaS3, MCF7, TMF1, and P388) revealed strong cytotoxicity comparable to that of adriamycin.

Lipid signaling in embryo implantation

A reciprocal interaction between the implantation-competent blastocyst and the receptive uterus is required for successful implantation. Although various molecular pathways are known to participate in this cross-talk, a comprehensive understanding of the implantation process is still missing. Gene expression studies and genetically engineered mouse models have provided evidence that lipid mediators serve as important signaling molecules in coordinating the series of events during early pregnancy including preimplantation embryo formation and development, implantation and postimplantation growth. This review focuses on the roles of two groups of lipid mediators, prostaglandins (PGs) and endocannabinoids, during early pregnancy. Our laboratory has shown that while PGs generated by the cPLA2-cyclooxygenase (COX) system are essential to ovulation, fertilization, and implantation, endocannabinoids are important for synchronizing preimplantation embryo development with uterine receptivity for implantation. A better understanding of these molecular signaling pathways is hoped to generate new strategies to correct implantation failure and improve pregnancy rates in women.

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.

CD40 engagement prevents peroxisome proliferator-activated receptor gamma agonist-induced apoptosis of B lymphocytes and B lymphoma cells by an NF-kappaB-dependent mechanism

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a transcription factor important in fat metabolism and is emerging as an important regulator of immunity and inflammation. We previously demonstrated that normal and malignant B lineage cells express PPARgamma and die by apoptosis after PPARgamma agonist exposure. In this study, we used the WEHI-231 mouse B lymphoma and normal mouse spleen B lymphocytes to elucidate the mechanism of PPARgamma agonist-induced apoptosis, and to determine whether an apoptosis rescue mechanism exists. In WEHI-231 cells, the natural PPARgamma agonist 15-deoxy-Delta(12,14)-PGJ(2) and the synthetic PPARgamma agonist ciglitazone induced activation of caspase 3 and caspase 9, a decrease in mitochondrial membrane potential, and caused cleavage of the caspase substrate poly(ADP-ribose) polymerase. We next tested whether CD40, whose engagement delivers a potent prosurvival signal for B cells, could protect B cells from PPARgamma agonist-induced apoptosis. CD40 engagement with CD40L significantly blunted the ability of PPARgamma agonists to induce apoptosis of B lymphocytes and prevented the inhibition of NF-kappaB mobilization by 15-deoxy-Delta(12,14)-PGJ(2) and ciglitazone. Interestingly, PPARgamma agonists induced an increase in IkappaBalpha and IkappaBbeta protein levels, which was prevented with CD40 engagement. The rescue mechanism induced by CD40 engagement was dependent on NF-kappaB, as an NF-kappaB inhibitor prevented rescue. Apoptosis induction by PPARgamma ligands may be important for immune regulation by killing B lymphocytes as a rapid means to dampen inflammation. Moreover, the ability of PPARgamma agonists to kill malignant B lineage cells has implications for their use as anti-B lymphoma agents.

Modulation of cytokine-induced cyclooxygenase 2 expression by PPARG ligands through NFkappaB signal disruption in human WISH and amnion cells

Cyclooxygenase (COX) activity increases in the human amnion in the settings of term and idiopathic preterm labor, contributing to the generation of uterotonic prostaglandins (PGs) known to participate in mammalian parturition. Augmented COX activity is highly correlated with increased COX2 (also known as prostaglandin-endoperoxide synthase 2, PTGS2) gene expression. We and others have demonstrated an essential role for nuclear factor kappaB (NFkappaB) in cytokine-driven COX2 expression. Peroxisome proliferator-activated receptor gamma (PPARG), a member of the nuclear hormone receptor superfamily, has been shown to antagonize NFkappaB activation and inflammatory gene expression, including COX2. We hypothesized that PPARG activation might suppress COX2 expression during pregnancy. Using primary amnion and WISH cells, we evaluated the effects of pharmacological (thiazolidinediones) and putative endogenous (15-deoxy-Delta(12,14)-prostaglandin J2, 15d-PGJ2) PPARG ligands on cytokine-induced NFkappaB activation, COX2 expression, and PGE2 production. We observed that COX2 expression and PGE2 production induced by tumor necrosis factor alpha (TNF) were significantly abrogated by 15d-PGJ2. The thiazolidinediones rosiglitazone (ROSI) and troglitazone (TRO) had relatively little effect on cytokine-induced COX2 expression except at high concentrations, at which these agents tended to increase COX2 abundance relative to cells treated with TNF alone. Interestingly, treatment with ROSI, but not TRO, led to augmentation of TNF-stimulated PGE2 production. Mechanistically, we observed that 15d-PGJ2 markedly diminished cytokine-induced activity of the NFkappaB transcription factor, whereas thiazolidinediones had no discernable effect on this system. Our data suggest that pharmacological and endogenous PPARG ligands use both receptor-dependent and -independent mechanisms to influence COX2 expression.

15d-PGJ2: the anti-inflammatory prostaglandin?

15-Deoxy-Delta-12,14-prostaglandin J2 (15d-PGJ2) is the most recently discovered prostaglandin. This cyclopentanone, the dehydration end product of PGD2, differs from other prostaglandins in several respects. There is no specific prostaglandin synthase (PGS) leading to 15d-PGJ2 production and no specific 15d-PGJ2 receptor has been identified to date. Instead, 15d-PGJ2 has been shown to act via PGD2 receptors (DP1 and DP2) and through interaction with intracellular targets. In particular, 15d-PGJ2 is recognized as the endogenous ligand for the intranuclear receptor PPARgamma. This property is responsible for many of the 15d-PGJ2 anti-inflammatory functions. In this review, we summarize the current understanding of 15d-PGJ2 synthesis, biology and main effects both in molecular physiology and pathological states.

The mitochondrial respiratory complex I is a target for 15-deoxy-delta12,14-prostaglandin J2 action

The prostaglandin J2 derivative 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) is a very active compound with important effects on inflammation, apoptosis, and cell growth processes. To exert this broad range of effects, 15d-PGJ2 binds and alters the activity of diverse proteins, which consequently are postulated to be mediators of its action. Among them are the transcription factors peroxisome proliferator-activated receptor gamma and nuclear factor kappaB, which are thought to play an essential role in the antitumorigenic and anti-inflammatory actions of 15d-PGJ2. Here, we show that 15d-PGJ2, at micromolar concentrations, efficiently blocks state 3 oxygen consumption in intact nonsynaptic mitochondria isolated from rat cerebral cortex. This effect is attributable to the inhibition by this prostaglandin of the activity of the enzyme NADH-ubiquinone reductase (complex I) of the mitochondrial respiratory chain. In addition to this, 15d-PGJ2 dramatically increases the rate of reactive oxygen species generation by complex I. The inhibition by 15d-PGJ2 of complex I activity was abolished by dithiothreitol, which raises the possibility that adduct formation with a critical component of complex I accounts for the inhibitory effect of this prostaglandin. These results clearly identified mitochondrial complex I as a new target for 15d-PGJ2 actions.