Contribution of cyclopentenone prostaglandins to the resolution of inflammation through the potentiation of apoptosis in activated macrophages

Targeting cyclooxygenase-2 for chemoprevention of inflammation-associated intestinal carcinogenesis: An update

Mounting evidence from preclinical and clinical studies suggests that persistent inflammation functions as a driving force in the journey to cancer. Cyclooxygenase-2 (COX-2) is a key enzyme involved in inflammatory signaling. While being transiently upregulated upon inflammatory stimuli, COX-2 has been found to be consistently overexpressed in human colorectal cancer and several other malignancies. The association between chronic inflammation and cancer has been revisited: cancer can arise when inflammation fails to resolve. Besides its proinflammatory functions, COX-2 also catalyzes the production of pro-resolving as well as anti-inflammatory metabolites from polyunsaturated fatty acids. This may account for the side effects caused by long term use of some COX-2 inhibitory drugs during the cancer chemopreventive trials. This review summarizes the latest findings highlighting the dual functions of COX-2 in the context of its implications in the development, maintenance, and progression of cancer.

Crosstalk between P2Y receptors and cyclooxygenase activity in inflammation and tissue repair

The role of extracellular nucleotides as modulators of inflammation and cell stress is well established. One of the main actions of these molecules is mediated by the activation of purinergic receptors (P2) of the plasma membrane. P2 receptors can be classified according to two different structural families: P2X ionotropic ion channel receptors, and P2Y metabotropic G protein-coupled receptors. During inflammation, damaged cells release nucleotides and purinergic signaling occurs along the temporal pattern of the synthesis of pro-inflammatory and pro-resolving mediators by myeloid and lymphoid cells. In macrophages under pro-inflammatory conditions, the expression and activity of cyclooxygenase 2 significantly increases and enhances the circulating levels of prostaglandin E2 (PGE2), which exerts its effects both through specific plasma membrane receptors (EP1-EP4) and by activation of intracellular targets. Here we review the mechanisms involved in the crosstalk between PGE2 and P2Y receptors on macrophages, which is dependent on several isoforms of protein kinase C and protein kinase D1. Due to this crosstalk, a P2Y-dependent increase in calcium is blunted by PGE2 whereas, under these conditions, macrophages exhibit reduced migratory capacity along with enhanced phagocytosis, which contributes to the modulation of the inflammatory response and tissue repair.

Biosynthesis of prostaglandin 15dPGJ2 -glutathione and 15dPGJ2-cysteine conjugates in macrophages and mast cells via MGST3

Inhibition of microsomal prostaglandin E synthase-1 (mPGES-1) results in decreased production of proinflammatory PGE₂ and can lead to shunting of PGH₂ into the prostaglandin D₂ (PGD₂)/15-deoxy-Δ^12,14-prostaglandin J₂ (15dPGJ₂) pathway. 15dPGJ₂ forms Michael adducts with thiol-containing biomolecules such as GSH or cysteine residues on target proteins and is thought to promote resolution of inflammation. We aimed to elucidate the biosynthesis and metabolism of 15dPGJ₂ via conjugation with GSH, to form 15dPGJ₂-glutathione (15dPGJ₂-GS) and 15dPGJ₂-cysteine (15dPGJ₂-Cys) conjugates and to characterize the effects of mPGES-1 inhibition on the PGD₂/15dPGJ₂ pathway in mouse and human immune cells. Our results demonstrate the formation of PGD₂, 15dPGJ₂, 15dPGJ₂-GS, and 15dPGJ₂-Cys in RAW264.7 cells after lipopolysaccharide stimulation. Moreover, 15dPGJ₂-Cys was found in lipopolysaccharide-activated primary murine macrophages as well as in human mast cells following stimulation of the IgE-receptor. Our results also suggest that the microsomal glutathione S-transferase 3 is essential for the formation of 15dPGJ₂ conjugates. In contrast to inhibition of cyclooxygenase, which leads to blockage of the PGD₂/15dPGJ₂ pathway, we found that inhibition of mPGES-1 preserves PGD₂ and its metabolites. Collectively, this study highlights the formation of 15dPGJ₂-GS and 15dPGJ₂-Cys in mouse and human immune cells, the involvement of microsomal glutathione S-transferase 3 in their biosynthesis, and their unchanged formation following inhibition of mPGES-1. The results encourage further research on their roles as bioactive lipid mediators.

15-Deoxy-△12,14-Prostaglandin J2 Promotes Resolution of Experimentally Induced Colitis

Uncontrolled macrophage functions cause failure to resolve gut inflammation and has been implicated in the pathogenesis of inflammatory bowel disease (IBD). 15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂), one of endogenous lipid mediators formed from arachidonic acid during the inflammatory process, has been reported to terminate inflammation. However, the pro-resolving effect of 15d-PGJ₂ on intestinal inflammation and underlying molecular mechanisms remain largely unknown. In the present study, we examined the effects of 15d-PGJ₂ on the resolution of dextran sulfate sodium (DSS)-induced murine colitis that mimics human IBD. Pharmacologic inhibition of prostaglandin D synthase (PGDS) responsible for the synthesis of 15d-PGJ₂ hampered resolution of inflammation in the colonic mucosa of mice treated with DSS. Notably, intraperitoneal injection of 15d-PGJ₂ accelerated the resolution of experimentally induced colitis. 15d-PGJ₂ treatment reduced the number of neutrophils and M1 macrophages, while it increased the proportion of M2 macrophages. Moreover, 15d-PGJ₂ treated mice exhibited the significantly reduced proportion of macrophages expressing the pro-inflammatory cytokine, IL-6 with concomitant suppression of STAT3 phosphorylation in the colonic mucosa of mice administered 2.5% DSS in drinking water. Taken together, these findings clearly indicate that 15d-PGJ₂, endogenously generated from arachidonic acid by cyclooxygenase-2 and PGDS activities in inflamed tissue, promotes resolution of intestinal colitis.

Specific Effects of Trabectedin and Lurbinectedin on Human Macrophage Function and Fate-Novel Insights

BACKGROUND

Tumor-associated macrophages (TAMs) play a crucial role in suppressing the immunosurveillance function of the immune system that prevents tumor growth. Indeed, macrophages can also be targeted by different chemotherapeutic agents improving the action over immune checkpoints to fight cancer. Here we describe the effect of trabectedin and lurbinectedin on human macrophage cell viability and function.

METHODS

Blood monocytes from healthy donors were differentiated into macrophages and exposed to different stimuli promoting functional polarization and differentiation into tumor-associated macrophages. Cells were challenged with the chemotherapeutic drugs and the effects on cell viability and function were analyzed.

RESULTS

Human macrophages exhibit at least two different profiles in response to these drugs. One-fourth of the blood donors assayed (164 individuals) were extremely sensitive to trabectedin and lurbinectedin, which promoted apoptotic cell death. Macrophages from other individuals retained viability but responded to the drugs increasing reactive oxygen production and showing a rapid intracellular calcium rise and a loss of mitochondrial oxygen consumption. Cell-membrane exposure of programmed-death ligand 1 (PD-L1) significantly decreased after treatment with therapeutic doses of these drugs, including changes in the gene expression profile of hypoxia-inducible factor 1 alpha (HIF-1α)-dependent genes, among other.

CONCLUSIONS

The results provide evidence of additional onco-therapeutic actions for these drugs.

The chemistry, biology and pharmacology of the cyclopentenone prostaglandins

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

Self-defense of macrophages against oxidative injury: Fighting for their own survival

Activated macrophages play a central role in both the development and resolution of inflammation. These immune cells need to be functional in harmful conditions with high levels of reactive oxygen and nitrogen species that can damage their basic cell components, which may alter their metabolism. An excessive accumulation of these cell alterations drives macrophages inexorably to cell death, which has been associated to the development of several inflammatory diseases and even with aging in a process termed as "immunosenescence". Macrophages, however, exhibit a prolonged survival in this hostile environment because they equip themselves with a complex network of protective mechanisms. Here we provide an overview of these self-defense mechanisms with special attention being paid to bioactive lipid mediators, NRF2 signaling and metabolic reprogramming.

The investigation of immunomodulatory effects of adipose tissue mesenchymal stem cell educated macrophages on the CD4 T cells

Mesenchymal stem cells (MSCs) are strong immunomodulatory cells investigated in numerous clinical studies on fatal pathologies, such as graft versus host disease and autoimmune diseases; e.g., systemic lupus erythematosus, Crohn's disease, and ulcerative colitis. Macrophages are one of the critical cells linking the innate and adaptive immune system, and it has been shown that MSCs can differentiate between pro-inflammatory M1 phenotype and anti-inflammatory M2 phenotype of macrophages. However, it has not yet been fully clarified whether these differentiated macrophages are functional. In this study, we compared the immunomodulatory effects on the CD4 T cells of M1, M2a and M2c macrophages with the macrophages that directly and indirectly cultured with MSCs. We analyzed the changes in CD14, CD64, CD80, CD163 and CD200R expression to evaluate macrophage phenotypes, and the changes in CD4, IFN-g, IL-4, IL-17a and FoxP3 expression to evaluate T helper subsets using the FACS method. The changes in IL-1b, IL-4, IL-10, IL-12p70, IL-17a and IFN-g in the media supernatants were analyzed using the Luminex method. We also performed WST-1 and Caspase-3 ELISA analyses to observe the proliferation and apoptosis status of the T cells. MSCs were found to differentiate macrophages into a distinctive phenotype, which was close to the M2c phenotype, but was not considered as an M2c cell due to the low expression of CD163, a characteristic marker for M2c. While MEM-D, MEM-ID and MSCs showed similar inhibitory effects on the Th2 and Th17 cells, the most significant increase in Treg cell frequencies was seen in MEM-D cells. Macrophages can alter their phenotypes and functions according to the stimuli from the environment. The fact that macrophages educated with MSCs suppressed the production of all the cytokines we evaluated even after the removal of MSCs suggests that these cells may be differentiated by MSCs into a suppressive macrophage subgroup. However, the Treg cell activation caused by direct interactions between MSCs and macrophage cells may be the most prominent observation of this study compared to previous work. As a result, according to our data, the interactions between MSCs and macrophages may lead to differentiation of macrophage cells into an immunosuppressive phenotype, and these macrophages may suppress the T lymphocyte subgroups at least as effectively as MSCs. However, our data obtained from in vitro experiments should be supported by future in vivo studies.

15-Lipoxygenase metabolites of α-linolenic acid, [13-(S)-HPOTrE and 13-(S)-HOTrE], mediate anti-inflammatory effects by inactivating NLRP3 inflammasome

The ratio of ω-6 to ω-3 polyunsaturated fatty acids (PUFAs) appears to be critical in the regulation of various pathophysiological processes and to maintain cellular homeostasis. While a high proportion of dietary intake of ω-6 PUFAs is associated with various inflammatory disorders, higher intake of ω-3 PUFAs is known to offer protection. It is now well established that beneficial effects of ω-3 PUFAs are mediated in part by their oxygenated metabolites mainly via the lipoxygenase (LOX) and cyclooxygenase (COX) pathways. However, the down-stream signaling pathways that are involved in these anti-inflammatory effects of ω-3 PUFAs have not been elucidated. The present study evaluates the effects of 15-LOX metabolites of α-linolenic acid (ALA, ω-3 PUFA) on lipopolysaccharide (LPS) induced inflammation in RAW 264.7 cells and peritoneal macrophages. Further, the effect of these metabolites on the survival of BALB/c mice in LPS mediated septic shock and also polymicrobial sepsis in Cecal Ligation and Puncture (CLP) mouse model was studied. These studies reveal the anti-inflammatory effects of 13-(S)-hydroperoxyoctadecatrienoic acid [13-(S)-HPOTrE] and 13-(S)-hydroxyoctadecatrienoic acid [13-(S)-HOTrE] by inactivating NLRP3 inflammasome complex through the PPAR-γ pathway. Additionally, both metabolites also deactivated autophagy and induced apoptosis. In mediating all these effects 13-(S)-HPOTrE was more potent than 13-(S)-HOTrE.

Cyclopentenone-containing oxidized phospholipids and their isoprostanes as pro-resolving mediators of inflammation

Inflammation represents a powerful innate immune response that defends tissue homeostasis. However, the appropriate termination of inflammatory processes is essential to prevent the development of chronic inflammatory disorders. The resolution of inflammation is actively induced by specialized pro-resolving lipid mediators, which include eicosanoids, resolvins, protectins and maresins. The responsible pro-resolution pathways have emerged as promising targets for anti-inflammatory therapies since they mitigate excessive inflammation without compromising the anti-microbial defenses of the host. We have recently shown that the lipid peroxidation of membrane phospholipids, which is associated with inflammatory conditions, generates oxidized phospholipid (OxPL) species with potent pro-resolving activities. These pro-resolving OxPLs contain a cyclopentenone as their common determinant, and are structurally and functionally related to endogenous pro-resolving prostaglandins. Here, we review the regulation of inflammatory responses by OxPLs with particular focus on the bioactivities and structural characteristics of cyclopentenone-OxPLs, and discuss the impact of the responsible signaling pathways on inflammatory diseases. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder.

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.

Immunomodulatory effects of Hedysarum polybotrys extract in mice macrophages, splenocytes and leucopenia

Astragali Radix (Huang-Qi) is a popular herbal medicine commonly used as a constituent in tonic herbal preparations. Hedysarum polybotrys Handel-Mazzetti is one species used of Astragali Radix. In this study, the immunomodulatory properties of H. polybotrys were explored by LPS-activated and SNP-treated RAW 264.7 cells and splenocytes and, daunoblastina-induced leucopenia BALB/c mice. Formononetin was used as the bioactive marker to monitor the quality of the H. polybotrys extracts. H. polybotrys was extracted with hot-water and methanol, and MeOH extract partitioned with H₂O (M-H) and ethyl acetate (M-EA) to yield four different fractions. M-EA had the highest formononetin and total proanthocyanidin content and showed stronger inhibitory effects on the production and expression of NO, PGE₂, iNOS and COX-2 in LPS-activated RAW 264.7 cells and splenocytes than the other fractions. In addition, M-EA significantly stimulated the proliferation of LPS-activated RAW 264.7 cells and splenocytes, enhanced NO radicals scavenging and attenuated NO-induced cytotoxicity. Furthermore, M-EA also significantly increased the rate of recovery of white blood cells level in daunoblastina-induced leucopenia mice. These evidences suggest that this traditional Qi-tonifying herb has potential effects in clinical conditions when immune-enhancing and anti-inflammatory effect is desired.

15-Deoxy-Δ12,14-prostaglandin J2 inhibits macrophage colonization by Salmonella enterica serovar Typhimurium

15-deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ₂) is an anti-inflammatory downstream product of the cyclooxygenase enzymes. It has been implicated to play a protective role in a variety of inflammatory mediated diseases, including rheumatoid arthritis, neural damage, and myocardial infarctions. Here we show that 15d-PGJ₂ also plays a role in Salmonella infection. Salmonella enterica Typhimurium is a Gram-negative facultative intracellular pathogen that is able to survive and replicate inside phagocytic immune cells, allowing for bacterial dissemination to systemic sites. Salmonella species cause a wide range of morbidity and mortality due to gastroenteritis and typhoid fever. Previously we have shown that in mouse models of typhoid fever, Salmonella infection causes a major perturbation in the prostaglandin pathway. Specifically, we saw that 15d-PGJ₂ production was significantly increased in both liver and feces. In this work we show that 15d-PGJ₂ production is also significantly increased in macrophages infected with Salmonella. Furthermore, we show that the addition of 15d-PGJ₂ to Salmonella infected RAW264.7, J774, and bone marrow derived macrophages is sufficient to significantly reduce bacterial colonization. We also show evidence that 15d-PGJ₂ is reducing bacterial uptake by macrophages. 15d-PGJ₂ reduces the inflammatory response of these infected macrophages, as evidenced by a reduction in the production of cytokines and reactive nitrogen species. The inflammatory response of the macrophage is important for full Salmonella virulence, as it can give the bacteria cues for virulence. The reduction in bacterial colonization is independent of the expression of Salmonella virulence genes SPI1 and SPI2, and is independent of the 15d-PGJ₂ ligand PPAR-γ. 15d-PGJ₂ also causes an increase in ERK1/2 phosphorylation in infected macrophages. In conclusion, we show here that 15d-PGJ₂ mediates the outcome of bacterial infection, a previously unidentified role for this prostaglandin.

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

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

Regulation of Glial Cell Functions by PPAR-gamma Natural and Synthetic Agonists

In the recent years, the peroxisome proliferator-activated receptor-γ (PPAR-γ), a well known target for type II diabetes treatment, has received an increasing attention for its therapeutic potential in inflammatory and degenerative brain disorders. PPAR-γ agonists, which include naturally occurring compounds (such as long chain fatty acids and the cyclopentenone prostaglandin 15-deoxy Δ^12,14 prostaglandin J₂), and synthetic agonists (among which the thiazolidinediones and few nonsteroidal anti-inflammatory drugs) have shown anti-inflammatory and protective effects in several experimental models of Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, multiple sclerosis and stroke, as well as in few clinical studies. The pleiotropic effects of PPAR-γ agonists are likely to be mediated by several mechanisms involving anti-inflammatory activities on peripheral immune cells (macrophages and lymphocytes), as well as direct effects on neural cells including cerebral vascular endothelial cells, neurons, and glia. In the present article, we will review the recent findings supporting a major role for PPAR-γ agonists in controlling neuroinflammation and neurodegeneration through their activities on glial cells, with a particular emphasis on microglial cells as major macrophage population of the brain parenchyma and main actors in brain inflammation.

Nonenzymatic free radical-catalyzed generation of 15-deoxy-Δ(12,14)-prostaglandin J₂-like compounds (deoxy-J₂-isoprostanes) in vivo

15-Deoxy-Δ(12,14)-prostaglandin J₂ (15-d-PGJ₂) is a reactive cyclopentenone eicosanoid generated from the dehydration of cyclooxygenase-derived prostaglandin D₂ (PGD₂). This compound possesses an α,β-unsaturated carbonyl moiety that can readily adduct thiol-containing biomolecules such as glutathione and cysteine residues of proteins via the Michael addition. Due to its reactivity, 15-d-PGJ₂ is thought to modulate inflammatory and apoptotic processes and is believed to be an endogenous ligand for peroxisome proliferator-activated receptor-γ. However, the extent to which 15-d-PGJ₂ is formed in vivo and the mechanisms that regulate its formation are unknown. Previously, we have reported the formation of PGD₂ and PGJ₂-like compounds, termed D₂/J₂-isoprostanes (D₂/J₂-IsoPs), produced in vivo by the free radical-catalyzed peroxidation of arachidonic acid (AA). Based on these findings, we investigated whether 15-d-PGJ₂-like compounds are also formed via this nonenzymatic pathway. Here we report the generation of novel 15-d-PGJ₂-like compounds, termed deoxy-J₂-isoprostanes (deoxy-J₂-IsoPs), in vivo, via the nonenzymatic peroxidation of AA. Levels of deoxy-J₂-IsoPs increased 12-fold (6.4 ± 1.1 ng/g liver) in rats after oxidant insult by CCl₄ treatment, compared with basal levels (0.55 ± 0.21 ng/g liver). These compounds may have important bioactivities in vivo under conditions associated with oxidant stress.

The natural antioxidant alpha-lipoic acid induces p27(Kip1)-dependent cell cycle arrest and apoptosis in MCF-7 human breast cancer cells

Unlike normal cells, tumor cells survive in a specific redox environment where the elevated reactive oxygen species contribute to enhance cell proliferation and to suppress apoptosis. Alpha-lipoic acid, a naturally occurring reactive oxygen species scavenger, has been shown to possess anticancer activity, due to its ability to suppress proliferation and to induce apoptosis in different cancer cell lines. Since at the moment little information is available regarding the potential effects of alpha-lipoic acid on breast cancer, in the present study we addressed the question whether alpha-lipoic acid induces cell cycle arrest and apoptosis in the human breast cancer cell line MCF-7. Moreover, we investigated some molecular mechanisms which mediate alpha-lipoic acid actions, focusing on the role of the PI3-K/Akt signalling pathway. We observed that alpha-lipoic acid is able to scavenge reactive oxygen species in MCF-7 cells and that the reduction of reactive oxygen species is followed by cell growth arrest in the G1 phase of the cell cycle, via the specific inhibition of Akt pathway and the up-regulation of the cyclin-dependent kinase inhibitor p27(kip1), and by apoptosis, via changes of the ratio of the apoptotic-related protein Bax/Bcl-2. Thus, the anti-tumor activity of alpha-lipoic acid observed in MCF-7 cells further stresses the role of redox state in regulating cancer initiation and progression.

N-acetylcysteine and 15 deoxy-{delta}12,14-prostaglandin J2 exert a protective effect against autoimmune thyroid destruction in vivo but not against interleukin-1{alpha}/interferon {gamma}-induced inhibitory effects in thyrocytes in vitro

Reactive oxygen species (ROS) are crucial for thyroid hormonogenesis, and their production is kept under tight control. Oxidative stress (OS) is toxic for thyrocytes in an inflammatory context. In vitro, Th1 pro-inflammatory cytokines have already been shown to decrease thyroid-specific protein expression. In the present study, OS level and its impact on thyroid function were analyzed in vitro in Th1 cytokine (interleukin [IL]-1alpha/interferon [IFN] gamma)-incubated thyrocytes (rat and human), as well as in vivo in thyroids from nonobese diabetic mice, a model of spontaneous autoimmune thyroiditis. N-acetylcysteine (NAC) and prostaglandin, 15 deoxy-(Delta12,14)-prostaglandinJ2 (15dPGJ2), were used for their antioxidant and anti-inflammatory properties, respectively. ROS production and OS were increased in IL-1alpha/IFNgamma-incubated thyrocytes and in destructive thyroiditis. In vitro, NAC not only reduced ROS production below control levels, but further decreased the expression of thyroid-specific proteins in addition to IL-1alpha/IFNgamma-inhibitory effects. Thus, besides ROS, other intracellular intermediaries likely mediate Th1 cytokine effects. In vivo, NAC and 15dPGJ2 reduced OS and the immune infiltration, thereby leading to a restoration of thyroid morphology. It is therefore likely that NAC and 15dPGJ2 mainly exert their protective effects by acting on infiltrating inflammatory cells rather than directly on thyrocytes.

Regulation of Nrf2-dependent gene expression by 15-deoxy-Delta12,14-prostaglandin J2

The J series of cyclopentenone prostaglandins (PGs) such as 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) are electrophilic lipid signaling mediators derived from the nonenzymatic dehydration of PGD(2), a major product of the cyclooxygenase pathway. The biological actions of 15d-PGJ(2) are attributed to its ability to form covalent adducts with thiol residues within specific signaling proteins, thus triggering redox-sensitive cell signaling pathways. One of the signaling pathways potently activated by 15d-PGJ(2) is the Keap1-Nrf2-ARE system, which has a well-appreciated role in protecting cells from endogenous and exogenous stresses as well as anti-inflammatory effects. In this review, we give an overview of the mechanisms by which 15d-PGJ(2) activates the Keap1-Nrf2-ARE system, focusing particularly on the role of Keap1 in sensing electrophilic stress. In addition, the Nrf2-dependent anti-inflammatory and cytoprotective effects of 15d-PGJ(2) are discussed.

Tripterine prevents endothelial barrier dysfunction by inhibiting endogenous peroxynitrite formation

BACKGROUND AND PURPOSE

Tripterine is an inhibitor of heat shock protein 90 and an active component of Tripterygium wilfordii Hook F., which is used in traditional Chinese medicine to treat inflammatory diseases such as rheumatoid arthritis. We hypothesized that tripterine inhibits endogenous peroxynitrite formation and thereby prevents endothelial barrier dysfunction.

EXPERIMENTAL APPROACH

Effects of tripterine were investigated on endothelial barrier function, inducible nitric oxide synthase (iNOS) expression, nicotinamide adenine dinucleotide phasphate (NADPH) oxidase activity, 3-nitrotyrosine formation, protein phosphatase type 2A (PP2A) activity, activation of extracellular-regulated kinase (ERK), c-Jun terminal kinase (JNK) and Janus kinase (Jak2), and degradation of IkappaB in microvascular endothelial cells exposed to pro-inflammatory stimulus [lipopolysaccharide (LPS) + interferon gamma (IFNgamma)] and on vascular permeability in air pouches of mice injected with LPS + IFNgamma.

KEY RESULTS

LPS + IFNgamma caused an increase in monolayer permeability, induction of iNOS and NADPH oxidase type 1 (Nox1) proteins, formation of superoxide, nitric oxide and 3-nitrotyrosine, and increase in PP2A activity in endothelial cells. These effects of LPS + IFNgamma were diminished by tripterine (50-200 nM). Further, LPS + IFNgamma-induced expression of iNOS and Nox1 was attenuated by the mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor PD98059, the JNK inhibitor SP600125, the Jak2 inhibitor AG490 and the NFkappaB inhibitor MG132, but not by the p38 mitogen-activated protein kinase inhibitor SB203580. LPS + IFNgamma stimulated phosphorylation of ERK, JNK and Jak2, and degradation of IkappaB, but only Jak2 phosphorylation was sensitive to tripterine (50-200 nM). Further, tripterine diminished the increased vascular permeability in inflamed air pouches.

CONCLUSION AND IMPLICATIONS

Our results indicate that, by preventing Jak2-dependent induction of iNOS and Nox1, tripterine inhibits peroxynitrite precursor synthesis, attenuates the increased activity of PP2A and consequently protects endothelial barrier function.

Ciglitazone induces apoptosis via activation of p38 MAPK and AIF nuclear translocation mediated by reactive oxygen species and Ca(2+) in opossum kidney cells

We have previously demonstrated that the synthetic peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist ciglitazone induces apoptosis accompanied by activation of p38 mitogen-activated protein kinase (MAPK) and nuclear translocation of apoptosis inducing factor (AIF) in opossum kidney (OK) renal epithelial cells. However, the precise mechanism by which ciglitazone induces activation of p38 MAPK and the role of AIF in the induction of the apoptosis are not defined. This study was therefore undertaken to determine whether the roles of reactive oxygen species (ROS) generation and intracellular Ca(2+) in the ciglitazone-induced activation of p38 MAPK and whether AIF nuclear translocation is responsible for the ciglitazone-induced apoptosis in OK renal epithelial cells. Ciglitazone caused generation of ROS and an increase in intracellular Ca(2+). Ciglitazone-induced cell death was reduced by the antioxidant Trolox, the Ca(2+) chelator EGTA, and the store-operated Ca(2+) channels (SOCC) blocker lanthanum chloride (La(3+)), indicating involvement of ROS and Ca(2+) in the ciglitazone-induced cell death. Ciglitazone-induced intracellular Ca(2+) increase was decreased by Trolox, while ROS generation was not affected by EGTA and La(3+), suggesting that ROS generation promote the increase of intracellular Ca(2+). Transfection of small interfering RNA (siRNA) of p38 MAPK or vector expressing microRNA (miRNA) of AIF prevented the ciglitazone-induced cell death. Activation of p38 MAPK, mitochondrial membrane depolarization, and AIF nuclear translocation induced by ciglitazone were inhibited by Trolox, EGTA and La(3+). Taken together, these results suggest that ROS-dependent intracellular Ca(2+) increase is responsible for activation of p38 MAPK and nuclear translocation of AIF by ciglitazone.

The importance of immune dysfunction in determining outcome in acute liver failure

Acute liver failure (ALF) shares striking similarities with septic shock with regard to the features of systemic inflammation, progression to multiple organ dysfunction and functional immunoparesis. While the existence of opposing systemic pro- and anti-inflammatory profiles resulting in organ failure and immune dysfunction are well recognised in septic shock, characterization of these processes in ALF has only recently been described. This review explores the evolution of the systemic inflammation in acute liver failure, its relation to disease progression, exacerbation of liver injury and development of innate immune dysfunction and extra-hepatic organ failure as sequelae. Defects in innate immunity are described in hepatic and extra-hepatic compartments. Clinical studies measuring levels of pro- and anti-inflammatory cytokines and expression of the antigen presentation molecule HLA-DR on monocytes, in combination with ex-vivo experiments, demonstrate that the persistence of a compensatory anti-inflammatory response syndrome, leading to functional monocyte deactivation, is a central event in the evolution of systemic immune dysfunction. Accurate immune profiling in ALF may permit the development of immunomodulatory strategies in order to improve outcome in this condition.

Salmonella enterica serovar Enteritidis dam mutant induces low NOS-2 and COX-2 expression in macrophages via attenuation of MAPK and NF-kappaB pathways

Although dam mutants of Salmonella have been proposed as live vaccines, their capacity to trigger cell inflammatory cascades has not been fully elucidated. We investigated in detail the ability of Salmonella enterica dam mutant to activate the signalling pathways of the inflammatory response in RAW 264.7 cells. Apoptosis in macrophages treated with Salmonella dam mutant was low. Similarly, the expression of both NOS-2 and COX-2 and subsequently the production of NO and PGE(2) was significantly reduced. Also, Salmonella dam mutant induced an attenuated activation of the inflammatory signalling pathway as indicated by the reduced degradation of IkappaBalpha and IkappaBbeta and the low IkappaBalpha phosphorylation found. In addition, translocation of p65 to the nucleus was notably impaired and the amount of phosphorylated p44, p42 and p38 MAPKs was clearly reduced in extracts from dam-infected macrophages. These results indicate that the lack of ERK and p38 phosphorylation at the proper time in dam-infected cells notably reduces the engagement of subsequent signalling pathways involved in the full activation of NF-kappaB in response to infection. Taken together, these results suggest that Salmonella activation of both signalling cascades in the inflammatory response is a mechanism requiring Dam protein participation.

PGJ2 antagonizes NF-kappaB-induced HIV-1 LTR activation in colonic epithelial cells

Intestinal epithelial cells play an important role in early stages of HIV-1 infection and long-term persistence of the virus. Here we determined the mechanism that regulates HIV-1 activation via prostaglandin J(2) (PGJ(2)) in Caco-2 cells. We showed that treatment of Caco-2 cells with PGJ(2) decreased the infectivity of a luciferase reporter virus, pHXB-luc, as well as HIV production following infection of cells with a X4-tropic virus by antagonizing sodium butyrate, a cellular activator known to induce HIV-1 transcription. Transfection of intestinal epithelial cells such as Caco-2, HT-29 and SW620 cells with full-length HIV-1 LTR (pLTR-luc) revealed that PGJ(2) reduced HIV-1 LTR-mediated reporter gene activity. The involvement of NF-kappaB in the PGJ(2)-dependent down-regulation of HIV-1 transcription was further assessed using the kappaB-regulated luciferase-encoding vectors. In Caco-2 cells, PGJ(2) decreased IKK activity, resulting in reduced NF-kappaB translocation to the nucleus. Since sodium butyrate has been associated with a chronic stress response in AIDS patients, our results suggest that addition of PGJ(2) in the environment of infected intestinal epithelial cells could reduce HIV-1 transcription.

Accumulation of 15-deoxy-delta(12,14)-prostaglandin J2 adduct formation with Keap1 over time: effects on potency for intracellular antioxidant defence induction

The COX (cyclo-oxygenase) pathway generates the reactive lipid electrophile 15d-PGJ2 (15-deoxy-Delta(12,14)-prostaglandin J2), which forms covalent protein adducts that modulate cell signalling pathways. It has been shown that this regulates important biological responses, including protection against oxidative stress, and supports the proposal that 15d-PGJ2 has pharmacological potential. Protective pathways activated by 15d-PGJ2 include those controlling the synthesis of the intracellular antioxidants GSH and the enzyme HO-1 (haem oxygenase-1). The induction of the synthesis of these intracellular antioxidants is, in large part, regulated by covalent modification of Keap1 (Kelchlike erythroid cell-derived protein with 'capn'collar homologyassociated protein 1) by the lipid and the subsequent activation of the EpRE (electrophile-response element). For the first time, we show that the potency of 15d-PGJ2 as a signalling molecule in endothelial cells is significantly enhanced by the accumulation of the covalent adduct with 15d-PGJ2 and endogenous Keap1 over the time of exposure to the prostaglandin. The consequence of this finding is that signalling initiated by electrophilic lipids differs from agonists that do not form covalent adducts with proteins because the constant generation of very lowconcentrations of 15d-PGJ2 can lead to induction of GSH or HO-1. In the course of these studies we also found that a substantial amount (97-99%) of exogenously added 15d-PGJ2 is inactivated in the medium and does not enter the cells to initiate cell signalling. In summary, we propose that the accumulation of covalent adduct formation with signalling proteins provides a mechanism through which endogenous intracellular formation of electrophilic lipids from COX can exert an anti-inflammatory effect in vivo.

Effects of telithromycin in in vitro and in vivo models of lipopolysaccharide-induced airway inflammation

BACKGROUND

The ketolide antibiotic telithromycin (TEL) exerts immunomodulatory and antiinflammatory effects in vitro and in a mouse model of septic shock. We studied the antiinflammatory activity of TEL in in vitro and in vivo models of airway inflammation induced by lipopolysaccharide (LPS).

METHODS

We measured the effects of TEL on the response of RAW 264.7 macrophages to LPS and of murine lung epithelial (MLE)-12 cells to supernatants of LPS-stimulated RAW 264.7 macrophages. Macrophage inflammatory protein (MIP)-2 and tumor necrosis factor (TNF)-alpha production, nuclear factor (NF)-kappaB activation, and apoptosis were determined. Acute airway inflammation was induced in untreated and TEL-treated BALB/c mice by nebulization with LPS. Total number of leukocytes, macrophages, and neutrophils, the protein concentration, and nitrite and cytokine levels were determined in the BAL fluid.

RESULTS

TEL inhibited in a dose-dependent manner the production of MIP-2 and TNF-alpha by LPS-stimulated RAW 264.7 macrophages, and the production of MIP-2 by MLE-12 epithelial cells to supernatants of LPS-stimulated RAW 264.7 macrophages. NF-kappaB activation was inhibited and apoptosis was increased in both cell lines by TEL. The LPS-induced influx of neutrophils in BAL fluid was decreased by TEL pretreatment. TEL also reduced protein, nitrite, MIP-2, and TNF-alpha levels in the BAL fluid of LPS-nebulized animals.

CONCLUSIONS

We have provided evidence that TEL exerts potent antiinflammatory effects in LPS-induced airways injury. We propose that TEL acts in the early phase of inflammation by reducing the release of inflammatory mediators through NF-kappaB inhibition, and in the later phase through enhancement of inflammatory cell apoptosis.

15-Deoxy-delta 12,14-prostaglandin J2 induces apoptosis via JNK-mediated mitochondrial pathway in osteoblastic cells

The cyclopentenone prostaglandin 15-deoxy-delta 12,14-prostaglandin J2 (15d-PGJ2) induces apoptosis in various cell types. However, the underlying mechanism of 15d-PGJ2-induced apoptosis is not fully understood. The present study was undertaken to determine the molecular mechanism by which 15d-PGJ2 induces apoptosis in MC3T3-E1 mouse osteoblastic cells. 15d-PGJ2 caused a concentration- and time-dependent apoptotic cell death. 15d-PGJ2 induced a transient activation of ERK1/2 and sustained activation of JNK. 15d-PGJ2-induced cell death was prevented by the JNK inhibitor SP6001, but not by inhibitors of ERK1/2 and p38. JNK activation by 15d-PGJ2 was blocked by antioxidants N-acetylcysteine (NAC) and GSH. 15d-PGJ2 caused ROS generation and 15d-PGJ2-induced cell death was prevented by antioxidants, suggesting involvement of ROS generation in 15d-PGJ2-induced cell death. 15d-PGJ2 triggered the mitochondrial apoptotic pathway indicated by enhanced Bax expression, loss of mitochondrial membrane potential, cytochrome c release, and caspase-3 activation. The JNK inhibitor blocked these events induced by 15d-PGJ2. Taken together, these results suggest that the 15d-PGJ2 induces cell death through the mitochondrial apoptotic pathway dependent of ROS and JNK activation in osteoblastic cells.

Oxidative stress in the thyroid gland: from harmlessness to hazard depending on the iodine content

In basal conditions, thyroid epithelial cells produce moderate amounts of reactive oxygen species (ROS) that are physiologically required for thyroid hormone synthesis. They are not necessarily toxic because they are continuously detoxified either in the process of hormone synthesis or by endogenous antioxidant systems. Using a rat model of goiter formation and iodine-induced involution, we found that compared with control thyroids, the oxidative stress, assessed by the detection of 4-hydroxynonenal, was strongly enhanced both in hyperplastic and involuting glands. The level of antioxidant defenses (glutathione peroxidases and peroxiredoxins) was also up-regulated in both groups, although somewhat less in the latter. Of note, increased oxidative stress came along with an inflammatory reaction, but only in involuting glands, suggesting that although antioxidant systems can adequately buffer a heavy load of ROS in goiter, it is not necessarily the case in involuting glands. The effects of 15-deoxy-Delta(12,14)-prostaglandin J2 (15dPGJ2), an endogenous ligand of peroxisome proliferated-activated receptor gamma (PPARgamma) with antiinflammatory properties, were then investigated in involuting glands. This drug strongly reduced both 4-hydroxynonenal staining and the inflammatory reaction, indicating that it can block iodine-induced cytotoxicity. When experiments were carried out with the PPARgamma antagonist, bisphenol A diglycidyl ether, 15dPGJ2-induced effects remained unchanged, suggesting that these effects were not mediated by PPARgamma. In conclusion, thyroid epithelial cells are well adapted to endogenously produced ROS in basal and goitrous conditions. In iodine-induced goiter involution, the increased oxidative stress is accompanied by inflammation that can be blocked by 15dPGJ2 through PPARgamma-independent protective effects.

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.

ERK-1/-2 and p38 kinase oppositely regulate 15-deoxy-delta(12,14)-prostaglandinJ(2)-Induced PPAR-gamma activation that mediates dedifferentiation but not cyclooxygenase-2 expression in articular chondrocytes

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is a ligand-activated transcription factor and plays an important role in growth, differentiation, and inflammation in different tissues. In this study, we investigated the effects of 15d-PGJ(2), a high-affinity ligand of PPAR-gamma, on dedifferentiation and on inflammatory responses such as COX-2 expression and PGE(2) production in rabbit articular chondrocytes with a focus on ERK-1/-2, p38 kinase, and PPAR-gamma activation. We report here that 15d-PGJ(2) induced dedifferentiation and/or COX-2 expression and subsequent PGE(2) production. 15d-PGJ(2) treatment stimulated activation of ERK-1/-2, p38 kinase, and PPAR-gamma. Inhibition of ERK-1/-2 with PD98059 recovered 15d-PGJ(2)-induced dedifferentiation and enhanced PPAR-gamma activation, whereas inhibition of p38 kinase with SB203580 potentiated dedifferentiation and partially blocked PPAR-gamma activation. Inhibition of ERK-1/-2 and p38 kinase abolished 15d-PGJ(2)-induced COX-2 expression and subsequent PGE(2) production. Our findings collectively suggest that ERK-1/-2 and p38 kinase oppositely regulate 15d-PGJ(2)-induced dedifferentiation through a PPAR-gamma-dependent mechanism, whereas COX-2 expression and PGE(2) production is regulated by ERK-1/-2 through a PPAR-gamma-independent mechanism but not p38 kinase in articular chondrocytes. Additionally, these data suggest that targeted modulation of the PPAR-gamma and mitogen-activated protein kinase pathway may offer a novel approach for therapeutic inhibition of joint tissue degradation.

Inflammation pro-resolving potential of 3,4-dihydroxyacetophenone through 15-deoxy-Δ12,14-prostaglandin J2 in murine macrophages

3,4-dihydroxyacetophenone (DHAP), an active component isolated from leaves of Tumaodongqing (Ilex Pubescens Hook. Et Arn. Var glaber Chang), is initially used to treat cardiovascular diseases. Previously, we found it had anti-inflammatory effect on macrophages by reducing the production of TNF-alpha in vitro. To further determine whether DHAP could influence inflammatory resolution, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2)), an arachidonic acid metabolite and also crucial pro-resolving mediator in inflammation, was chosen as the research target. It showed that 10(-5) M DHAP resulted in obvious increase of 15dPGJ(2) in LPS-activated macrophages. Further, inflammation related cytokines and cell apoptosis were also studied. We found DHAP could markedly inhibit LPS-stimulated production of TNF-alpha. However, it could not change the level of IL-10 obviously. At the same time, LPS-triggered apoptosis of macrophage was enhanced by DHAP significantly. After different kinds of cyclooxygenase (COX) inhibitors were administrated, it showed that the effects of DHAP on TNF-alpha and apoptosis were COX-2 dependent. While, inhibition of both COX-1 and COX-2 with indomethacin and administration of 15dPGJ(2) simultaneous reserved the effect of DHAP to inhibit TNF-alpha and enhance apoptosis in LPS-activated macrophages at least partly. The level of COX-2 mRNA and protein were also detected. It was showed that DHAP could increase the expression of COX-2 at both mRNA and protein levels in LPS-activated macrophages. Our results suggest that DHAP could accelerate resolution phase of acute inflammation though enhance the production of 15dPGJ(2), which was also proved to mediate the function of DHAP to inhibit TNF-alpha and enhance apoptosis in vitro. These results are potentially valuable for future use of DHAP.

Kaurane diterpenes protect against apoptosis and inhibition of phagocytosis in activated macrophages

BACKGROUND AND PURPOSE

The kaurane diterpenes foliol and linearol are inhibitors of the activation of nuclear factor kappaB, a transcription factor involved in the inflammatory response. Effects of these diterpenes on apoptosis and phagocytosis have been analysed in cultured peritoneal macrophages and in the mouse macrophage cell line, RAW 264.7.

EXPERIMENTAL APPROACH

Macrophages were maintained in culture and activated with pro-inflammatory stimuli in the absence or presence of diterpenes. Apoptosis and the phagocytosis in these cells under these conditions were determined.

KEY RESULTS

Incubation of macrophages with a mixture of bacterial lipopolysaccharide (LPS)/interferon-gamma (IFN-gamma) induced apoptosis through a NO-dependent pathway, an effect significantly inhibited by foliol and linearol in the low muM range, without cytotoxic effects. Apoptosis in macrophages induced by NO donors was also inhibited. The diterpenes prevented apoptosis through a mechanism compatible with the inhibition of caspase-3 activation, release of cytochrome c to the cytosol and p53 overexpression, as well as an alteration in the levels of proteins of the Bcl-2 family, in particular, the levels of Bax. Cleavage of poly(ADP-ribose) polymerase, a well-established caspase substrate, was reduced by these diterpenes. Treatment of cells with foliol and linearol decreased phagocytosis of zymosan bioparticles by RAW 264.7 cells and to a greater extent by peritoneal macrophages.

CONCLUSIONS AND IMPLICATIONS

Both diterpenes protected macrophages from apoptosis and inhibited phagocytosis, resulting in a paradoxical control of macrophage function, as viability was prolonged but inflammatory and phagocytic functions were impaired.

Accumulation of hypoxia-inducible factor-1alpha through a novel electrophilic, thiol antioxidant-sensitive mechanism

15-deoxy-Delta(12,14)-prostaglandin-J(2) (15d-PGJ(2)) is a peroxisome-activated proliferator receptor-gamma (PPARgamma) agonist which contains an alpha,beta-unsaturated electrophilic ketone involved in nucleophilic addition reactions to thiols. Here we studied its effect on hypoxia-inducible factor-1alpha (HIF-1alpha) in human proximal tubular cells HK-2. 15d-PGJ(2) induced stabilization of HIF-1alpha protein, without affecting HIF-1alpha mRNA levels or proteasome activity, leading to its nuclear accumulation and activation of HIF-induced transcription. Accumulation of HIF-1alpha was unaffected by selective PPARgamma blockade nor mimicked by the PPARgamma agonists ciglitazone and 9,10-dihydro-15d-PGJ(2). N-acetylcysteine, reduced glutathione (GSH) or dithiothreitol (i.e. agents that act as thiol reducing agents and/or increase the GSH content), but not reactive oxygen species (ROS) scavengers, prevented 15d-PGJ(2)-induced HIF-1alpha accumulation whereas the inhibitor of GSH synthesis buthionine sulfoximine cooperated with 15d-PGJ(2) to accumulate HIF-1alpha. Finally, HIF-1alpha expression was increased by the electrophilic alpha,beta-unsaturated compounds acrolein and PGA(2), but not by 9,10-dihydro-15d-PGJ(2), which lacks the electrophilic cyclopentenone moiety. Taken together, these results point out to a new mechanism to increase pharmacologically the cell levels of HIF-1alpha through the electrophilic reaction of alpha,beta-unsaturated ketones with thiol groups.

15-deoxy-Delta12,14-prostaglandin J2 negatively regulates rankl gene expression in activated T lymphocytes: role of NF-kappaB and early growth response transcription factors

Receptor activator of NF-kappaB ligand (RANKL) and its receptor RANK are cell surface proteins abundantly expressed in bone and lymphoid tissues, whose interaction triggers different signaling pathways leading to activation and differentiation of osteoclasts, pivotal actors of the normal bone remodeling cycle. Moreover, RANKL may act as an immunomodulator, representing an important dendritic cell survival factor produced by activated T cells. A large body of research has shown that not only does the RANKL/RANK system regulate the physiology of bone development but also plays an important pathological role in bone destruction mediated by inflammatory disorders or bone metastatic tumors. 15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) is a cyclopentenone-type PG endowed with anti-inflammatory properties and produced by different cells, including those of the immune system. Although 15d-PGJ(2) has been studied as a natural ligand of the peroxisome proliferator-activated receptor-gamma nuclear receptor, relevant peroxisome proliferator-activated receptor-gamma-independent actions mediated by this prostanoid have been described. In this study, we describe the effect of 15d-PGJ(2) on the expression of the rankl gene in T lymphocytes. We show that 15d-PGJ(2) inhibits rankl mRNA expression, protein, and rankl promoter activity by mechanisms mediated by its chemically reactive cyclopentenone moiety. Our data also indicate that 15d-PGJ(2) represses rankl activation by interfering with the expression and/or activity of the transcription factors NF-kappaB, early growth response-2, and early growth response-3, whose altered balancing and transactivation may contribute for the repression of this gene. These results place rankl as a novel molecular target for the different immunoregulatory activities mediated by 15d-PGJ(2). The physiological and pharmacological implications of these observations are discussed.

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.

Prostanoids with cyclopentenone structure as tools for the characterization of electrophilic lipid-protein interactomes

Electrophilic eicosanoids arise from the free radical-induced peroxidation of arachidonic acid or its metabolites. These reactive species may play an important role in pathophysiological processes associated with inflammation and oxidative stress. Cyclopentenone prostaglandins (cyPG) and isoprostanes are reactive eicosanoids that can form covalent adducts with cysteine residues in proteins through Michael addition. In pharmacological studies, cyPG have shown potent protective effects in experimental models of inflammation and tissue injury, and they have been proposed to contribute to inflammatory resolution. An important mechanism for the anti-inflammatory effects of cyPG is the covalent modification of critical cysteine residues in proteins involved in the modulation of inflammation, such as transcription factors NF-kappaB and AP-1. In recent years, analogs of electrophilic prostanoids have been used in various approaches to identify biologically relevant protein targets for this modification. Prostanoids with cyclopentenone structure have been shown to target a defined subproteome that is beginning to be characterized. Structural studies suggest that diverse cyPG may modify distinct proteins selectively. Functional studies put forward a dual role for these compounds in the cellular response to inflammation or stress. Therefore, a detailed knowledge of targets of electrophilic eicosanoids and the functional consequences of their modification will contribute to the understanding of their mechanism of action and help assess whether these endogenous mediators can be exploited as the basis for the development of novel therapeutic strategies. In this article we discuss the recent advances in this rapidly growing field.

Contrary prostaglandins: the opposing roles of PGD2 and its metabolites in leukocyte function

Traditionally, PGD(2) has been considered to be a pro-inflammatory mediator, acting via classical PG receptors, such as the PGD(2) receptor (DP). PGD(2) is degraded rapidly in vitro and in vivo to a variety of metabolites, the majority of which were thought, until recently, to be physiologically inactive. Several "inactive" metabolites, particularly 15d-PGJ(2), have been shown to have wide-ranging effects on leukocytes and other cell types, however, and a potentially important anti-inflammatory role for PGD(2) has now been recognized, and the complexity of PGD(2) signaling is beginning to be elucidated. PGD(2) and its metabolites are biologically active over a broad concentration range, and, intriquingly, it appears that there are marked concentration-dependent variations in the consequences of signaling by these eicosanoids, which have the potential to exert pro- and anti-inflammatory effects. For example, the actions of PGD(2) can influence multiple stages in the life of the mature eosinophil, from causing its release from the bone marrow to inducing its recruitment and activation and, ultimately, regulating its apoptosis. This review is concerned with the diverse responses induced in leukocytes by PGD(2) and its metabolites and the signaling mechanisms which are thought to be responsible for them.

Mechanisms of cell death in oxidative stress

Reactive oxygen or nitrogen species (ROS/RNS) generated endogenously or in response to environmental stress have long been implicated in tissue injury in the context of a variety of disease states. ROS/RNS can cause cell death by nonphysiological (necrotic) or regulated pathways (apoptotic). The mechanisms by which ROS/RNS cause or regulate apoptosis typically include receptor activation, caspase activation, Bcl-2 family proteins, and mitochondrial dysfunction. Various protein kinase activities, including mitogen-activated protein kinases, protein kinases-B/C, inhibitor-of-I-kappaB kinases, and their corresponding phosphatases modulate the apoptotic program depending on cellular context. Recently, lipid-derived mediators have emerged as potential intermediates in the apoptosis pathway triggered by oxidants. Cell death mechanisms have been studied across a broad spectrum of models of oxidative stress, including H2O2, nitric oxide and derivatives, endotoxin-induced inflammation, photodynamic therapy, ultraviolet-A and ionizing radiations, and cigarette smoke. Additionally ROS generated in the lung and other organs as the result of high oxygen therapy or ischemia/reperfusion can stimulate cell death pathways associated with tissue damage. Cells have evolved numerous survival pathways to counter proapoptotic stimuli, which include activation of stress-related protein responses. Among these, the heme oxygenase-1/carbon monoxide system has emerged as a major intracellular antiapoptotic mechanism.

Addition of electrophilic lipids to actin alters filament structure

Pathophysiological processes associated with oxidative stress lead to the generation of reactive lipid species. Among them, lipids bearing unsaturated aldehyde or ketone moieties can form covalent adducts with cysteine residues and modulate protein function. Through proteomic techniques we have identified actin as a target for the addition of biotinylated analogs of the cyclopentenone prostaglandins 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) and PGA(1) in NIH-3T3 fibroblasts. This modification could take place in vitro and mapped to the protein C-terminal end. Other electrophilic lipids, like the isoprostane 8-iso-PGA(1) and 4-hydroxy-2-nonenal, also bound to actin. The C-terminal region of actin is important for monomer-monomer interactions and polymerization. Electron microscopy showed that actin treated with 15d-PGJ(2) or 4-hydroxy-2-nonenal formed filaments which were less abundant and displayed shorter length and altered structure. Streptavidin-gold staining allowed mapping of biotinylated 15d-PGJ(2) at sites of filament disruption. These results shed light on the structural implications of actin modification by lipid electrophiles.

Contrasting roles for reactive oxygen species and nitric oxide in the innate response to pulmonary infection with Streptococcus pneumoniae

The pulmonary innate response to low-dose bacterial challenge requires functioning alveolar macrophages (AM) but also subsequent macrophage apoptosis. To address the role of reactive oxygen species (ROS) and nitric oxide (NO) in AM apoptosis, sub-clinical Streptococcus pneumoniae infection was established in gp91(phox-/-) and inducible NO synthase deficient (iNOS(-/-)) mice. Both AM apoptosis and the number of macrophages containing apoptotic bodies are reduced in iNOS(-/-) as compared to control or gp91(phox-/-) mice. iNOS(-/-) mice recruit neutrophils and generate TNF-alpha to compensate for impaired AM competence but ROS deficiency has no apparent effect on AM function in this model.

Specific contribution of p19(ARF) to nitric oxide-dependent apoptosis

NO is an important bioactive molecule involved in a variety of physio- and pathological processes, including apoptosis induction. The proapoptotic activity of NO involves the rise in the tumor suppressor p53 and the accumulation and targeting of proapoptotic members of the Bcl-2 family, in particular Bax and the release of cytochrome c from the mitochondria. However, the exact mechanism by which NO induces p53 activation has not been fully elucidated. In this study, we describe that NO induces p19(ARF) through a transcriptional mechanism. This up-regulation of p19(ARF) activates p53, leading to apoptosis. The importance of p19(ARF) on NO-dependent apoptosis was revealed by the finding that various cell types from alternate reading frame-knockout mice exhibit a diminished response to NO-mediated apoptosis when compared with normal mice. Moreover, the biological relevance of alternative reading frame to p53 apoptosis was confirmed in in vivo models of apoptosis. Together, these results demonstrate that NO-dependent apoptosis requires, in part, the activation of p19(ARF).

Interleukin-13 enhances cyclooxygenase-2 expression in activated rat brain microglia: implications for death of activated microglia

Brain inflammation has recently attracted widespread interest because it is a risk factor for the onset and progression of brain diseases. In this study, we report that cyclooxygenase-2 (COX-2) plays a key role in the resolution of brain inflammation by inducing the death of microglia. We previously reported that IL-13, an anti-inflammatory cytokine, induced the death of activated microglia. These results revealed that IL-13 significantly enhanced COX-2 expression and production of PGE(2) and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) in LPS-treated microglia. Two other anti-inflammatory cytokines, IL-10 and TGF-beta, neither induced microglial death nor enhanced COX-2 expression or PGE(2) or 15d-PGJ(2) production. Therefore, we hypothesized that the effect of IL-13 on COX-2 expression may be linked to death of activated microglia. We found that COX-2 inhibitors (celecoxib and NS398) suppressed the death of microglia induced by a combination of LPS and IL-13 and that exogenous addition of PGE(2) and 15d-PGJ(2) induced microglial death. Agonists of EP2 (butaprost) and peroxisome proliferator-activated receptor gamma (ciglitazone) mimicked the effect of PGE(2) and 15d-PGJ(2), and an EP2 antagonist (AH6809) and a peroxisome proliferator-activated receptor gamma antagonist (GW9662) suppressed microglial death induced by LPS in combination with IL-13. In addition, IL-13 potentiated LPS-induced activation of JNK, and the JNK inhibitor SP600125 suppressed the enhancement of COX-2 expression and attenuated microglial death. Taken together, these results suggest that IL-13 enhanced COX-2 expression in LPS-treated microglia through the enhancement of JNK activation. Furthermore, COX-2 products, PGE(2) and 15d-PGJ(2), caused microglial death, which terminates brain inflammation.

15-Deoxy-Δ12,14-prostaglandin J2 suppresses IL-6-induced STAT3 phosphorylation via electrophilic reactivity in endothelial cells

In this study, the effects of 15d-PGJ(2) were investigated in IL-6-activated endothelial cells (ECs). 15d-PGJ(2) was found to abrogate phosphorylation on tyr705 of STAT3 in IL-6-treated ECs, in a dose- and time-dependent manner, but did not inhibit serine phosphorylation of STAT3 and the upperstream JAK2 phosphorylation. Other PPAR activators, such as WY1643 or ciglitazone, had no effect upon IL-6-induced STAT3 phosphorylation. Additionally, neither orthovanadate nor l-NAME treatment reverses the inhibition of STAT3 phosphorylation by 15d-PGJ(2). Otherwise, the effect of 15d-PGJ(2) requires the alpha,beta-unsaturated carbonyl group in the cyclopentane ring. A 15d-PGJ(2) analog, 9,10-Dihydro-15d-PGJ(2), which lack alpha,beta-unsaturated carbonyl group showed no increase in ROS production and no effect in inhibition of IL-6-induced STAT3 phosphorylation. The electrophilic compound, acrolein, mimics the inhibition effect of 15d-PGJ(2). Among the antioxidants, only NAC and glutathione reversed the effects of 15d-PGJ(2). NAC, glutathione and DTT all reversed the inhibition of STAT3 phosphorylation when preincubated with 15d-PGJ(2). The inhibition of ICAM-1 gene expression by 15d-PGJ(2) was abrogated by NAC and glutathione in IL-6-treated ECs. Taken together, these results suggest that 15d-PGJ(2) inhibits IL-6-stimulated phosphorylation on tyr705 of STAT3 dependent on its own electrophilic reactivity in ECs.

Positioning prostanoids of the D and J series in the immunopathogenic scheme

Prostaglandin D(2) (PGD(2)) is produced by a variety of immune and non-hematopoietic cells and appears to function in both an inflammatory and homeostatic capacity. Two genetically distinct PGD(2)-synthesizing enzymes have been identified to date, including hematopoietic- and lipocalin-type PGD synthases (H-PGDS and L-PGDS, respectively). Though the inter-species expression profiles of these two enzymes vary widely, H-PGDS is generally localized to the cytosolic aspect of immune and inflammatory cells, whereas L-PGDS is more resigned to tissue-based expression. PGD(2) activity is principally mediated through two unique G protein-coupled receptors (GPCR), designated DP(1) and DP(2). These receptors exhibit overlapping binding profiles, yet their respective agonists elicit generally distinctive responses. Additional to DP receptors, the PGD(2) metabolite 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) binds the nuclear peroxisome proliferator-activated receptor gamma (PPARgamma) and has the facility to initiate a variety of anti-inflammatory phenotypes either through or independent of PPARgamma association. This review highlights the collective relevance of PGD(2) and its respective synthases, receptors, and metabolites in immunopathologic responses.

Rosiglitazone and 15-deoxy-Delta12,14-prostaglandin J2 cause potent neuroprotection after experimental stroke through noncompletely overlapping mechanisms

Stroke triggers an inflammatory cascade which contributes to a delayed cerebral damage, thus implying that antiinflammatory strategies might be useful in the treatment of acute ischaemic stroke. Since two unrelated peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists, the thiazolidinedione rosiglitazone (RSG) and the cyclopentenone prostaglandin 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2), have been shown to possess antiinflammatory properties, we have tested their neuroprotective effects in experimental stroke. Rosiglitazone or 15d-PGJ2 were administered to rats 10 mins or 2 h after permanent middle cerebral artery occlusion (MCAO). Stroke outcome was evaluated by determination of infarct volume and assessment of neurological scores. Brains were collected for protein expression, gene array analyses and gene shift assays. Our results show that both compounds decrease MCAO-induced infarct size and improve neurological scores. At late times, the two compounds converge in the inhibition of MCAO-induced brain expression of inducible NO synthase and the matrix metalloproteinase 9. Interestingly, at early times, complementary DNA microarrays and gene shift assays show that different mechanisms are recruited. Analysis of early nuclear p65 and late cytosolic IkappaBalpha protein levels shows that both compounds inhibit nuclear factor-kappaB signalling, although at different levels. All these results suggest both PPARgamma-dependent and independent pathways, and might be useful to design both therapeutic strategies and prognostic markers for stroke.

The role of IL-1 and IL-1Ra in joint inflammation and cartilage degradation

Interleukin (IL)-1 is a cytokine that plays a major role in inflammatory responses in the context of infections and immune-mediated diseases. IL-1 refers to two different cytokines, termed IL-1alpha and IL-1beta, produced from two genes. IL-1alpha and IL-1beta are produced by different cell types following stimulation by bacterial products, cytokines, and immune complexes. Monocytes/macrophages are the primary source of IL-1beta. Both cytokines do not possess leader peptide sequences and do not follow a classical secretory pathway. IL-1alpha is mainly cell associated, whereas IL-1beta can be released from activated cells after cleavage of its amino-terminal region by caspase-1. IL-1 is present in the synovial tissue and fluids of patients with rheumatoid arthritis. Several in vitro studies have shown that IL-1 stimulates the production of mediators such as prostaglandin E(2), nitric oxide, cytokines, chemokines, and adhesion molecules that are involved in articular inflammation. Furthermore, IL-1 stimulates the synthesis and activity of matrix metalloproteinases and other enzymes involved in cartilage destruction in rheumatoid arthritis and osteoarthritis. The effects of IL-1 are inhibited in vitro and in vivo by natural inhibitors such as IL-1 receptor antagonist and soluble receptors. IL-1 receptor antagonist belongs to the IL-1 family of cytokines and binds to IL-1 receptors but does not induce any intracellular response. IL-1 receptor antagonist inhibits the effect of IL-1 by blocking its interaction with cell surface receptors. The use of IL-1 inhibitors in experimental models of inflammatory arthritis and osteoarthritis has provided a strong support for the role of IL-1 in the pathogeny of these diseases. Most importantly, these findings have been confirmed in clinical trials in patients with rheumatic diseases. Additional strategies aimed to block the effect of IL-1 are tested in clinical trials.

Reactive lipid species from cyclooxygenase-2 inactivate tumor suppressor LKB1/STK11: cyclopentenone prostaglandins and 4-hydroxy-2-nonenal covalently modify and inhibit the AMP-kinase kinase that modulates cellular energy homeostasis and protein translation

LKB1, a unique serine/threonine kinase tumor suppressor, modulates anabolic and catabolic homeostasis, cell proliferation, and organ polarity. Chemically reactive lipids, e.g. cyclopentenone prostaglandins, formed a covalent adduct with LKB1 in MCF-7 and RKO cells. Site-directed mutagenesis implicated Cys210 in the LKB1 activation loop as the residue modified. Notably, ERK, JNK, and AKT serine/threonine kinases with leucine or methionine, instead of cysteine, in their activation loop did not form a covalent lipid adduct. 4-Hydroxy-2-nonenal, 4-oxo-2-nonenal, and cyclopentenone prostaglandin A and J, which all contain alpha,beta-unsaturated carbonyls, inhibited the AMP-kinase kinase activity of cellular LKB1. In turn, this attenuated signals throughout the LKB1 --> AMP kinase pathway and disrupted its restraint of ribosomal S6 kinases. The electrophilic beta-carbon in these lipids appears to be critical for inhibition because unreactive lipids, e.g. PGB1, PGE2, PGF2alpha, and TxB2, did not inhibit LKB1 activity (p > 0.05). Ectopic expression of cyclooxygenase-2 and endogenous biosynthesis of eicosanoids also inhibited LKB1 activity in MCF-7 cells. Our results suggested a molecular mechanism whereby chronic inflammation or oxidative stress may confer risk for hypertrophic or neoplastic diseases. Moreover, chemical inactivation of LKB1 may interfere with its physiological antagonism of signals from growth factors, insulin, and oncogenes.