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

Human multiple myeloma cells express peroxisome proliferator-activated receptor gamma and undergo apoptosis upon exposure to PPARgamma ligands

Multiple myeloma is essentially an incurable malignancy and it is therefore of great interest to develop new therapeutic approaches. We previously reported that human B cell-lymphomas express the nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) and are killed by PPARgamma ligands. Herein, we investigate the therapeutic potential of PPARgamma ligands for multiple myeloma. The human multiple myeloma cell lines ANBL6 and 8226 express PPARgamma mRNA and protein. The PPARgamma ligands, 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) and ciglitazone, induced multiple myeloma cell apoptosis as determined by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, loss of mitochondrial membrane potential, and caspase activation. Importantly, the ability of PPARgamma ligands to kill both multiple myeloma cell lines was not abrogated by Interleukin-6 (IL-6), a multiple myeloma growth survival factor. Finally, the RXR ligand 9-cis retinoic acid (9-cis RA) in combination with PPARgamma ligands greatly enhanced multiple myeloma cell killing. These new findings support that PPARgamma ligands may represent a novel therapy for multiple myeloma.

Prostaglandin A2-mediated stabilization of p21 mRNA through an ERK-dependent pathway requiring the RNA-binding protein HuR

Treatment with the stress agent prostaglandin A2 (PGA2) induces expression of the cyclin-dependent kinase inhibitor p21. Here, we present evidence that p21 expression increases through PGA2-triggered stabilization of the p21 mRNA and further show that these events require the mitogen-activated protein (MAP) kinase ERK. Binding experiments using either endogenous p21 mRNA or in vitro-labeled p21 transcripts revealed a specific PGA2-dependent association of the p21 mRNA with the RNA-binding protein HuR. Interestingly, although inhibition of the ERK pathway did not prevent the PGA2-triggered increase in cytoplasmic HuR, it did impair the formation of endogenous and in vitro [HuR-p21 mRNA] complexes and further prevented the PGA2-mediated stabilization of the p21 mRNA, suggesting that ERK-mediated events were required for binding HuR to the p21 mRNA and preventing its decay. RNA interference-based knockdown of HuR abundance further served to demonstrate the contribution of HuR-mediated p21 mRNA stabilization toward enhancing p21 expression after PGA2 treatment. Collectively, our results indicate that PGA2 stabilizes the p21 mRNA through an ERK-independent increase in cytoplasmic HuR levels and an ERK-dependent association of HuR with the p21 mRNA.

Environmental and Endogenous Peroxisome Proliferator-Activated Receptor γ Agonists Induce Bone Marrow B Cell Growth Arrest and Apoptosis: Interactions between Mono(2-ethylhexyl)phthalate, 9-cis-Retinoic Acid, and 15-Deoxy-Δ12,14-prostaglandin J2

The common commercial use of phthalate esters has resulted in significant human exposure to these bioactive compounds. The facts that phthalate ester metabolites, like endogenous PGs, are peroxisome proliferator-activated receptor (PPAR) agonists, and that PPARgamma agonists induce lymphocyte apoptosis suggest that phthalate esters are immunosuppressants that could act together with PGs to modulate early B cell development. In this study we examined the effects of a metabolite of one environmental phthalate, mono(2-ethylhexyl)phthalate (MEHP), and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), on developing B cells. MEHP inhibited [(3)H]thymidine incorporation by primary murine bone marrow B cells and a nontransformed murine pro/pre-B cell line (BU-11). Cotreatment with a retinoid X receptor alpha ligand, 9-cis-retinoic acid, decreased [(3)H]thymidine incorporation synergistically, thereby implicating activation of a PPARgamma-retinoid X receptor alpha complex. These results were similar to those obtained with the natural PPARgamma ligand 15d-PGJ(2). At moderate MEHP concentrations (25 or 100 microM for primary pro-B cells and a pro/pre-B cell line, respectively), inhibition of [(3)H]thymidine incorporation resulted primarily from apoptosis induction, whereas at lower concentrations, the inhibition probably reflected growth arrest without apoptosis. Cotreatment of bone marrow B cells with 15d-PGJ(2) and MEHP significantly enhanced the inhibition of [(3)H]thymidine incorporation seen with MEHP alone, potentially mimicking exposure in the bone marrow microenvironment where PG concentrations are high. Finally, MEHP- and 15d-PGJ(2)-induced death does not result from a decrease in NF-kappaB activation. These data demonstrate that environmental phthalates can cooperate with an endogenous ligand, 15d-PGJ(2), to inhibit proliferation of and induce apoptosis in developing bone marrow B cells, potentially via PPARgamma activation.

Cellular mechanisms of redox cell signalling: role of cysteine modification in controlling antioxidant defences in response to electrophilic lipid oxidation products

The molecular mechanisms through which oxidized lipids and their electrophilic decomposition products mediate redox cell signalling is not well understood and may involve direct modification of signal-transduction proteins or the secondary production of reactive oxygen or nitrogen species in the cell. Critical in the adaptation of cells to oxidative stress, including exposure to subtoxic concentrations of oxidized lipids, is the transcriptional regulation of antioxidant enzymes, many of which are controlled by antioxidant-responsive elements (AREs), also known as electrophile-responsive elements. The central regulator of the ARE response is the transcription factor Nrf2 (NF-E2-related factor 2), which on stimulation dissociates from its cytoplasmic inhibitor Keap1, translocates to the nucleus and transactivates ARE-dependent genes. We hypothesized that electrophilic lipids are capable of activating ARE through thiol modification of Keap1 and we have tested this concept in an intact cell system using induction of glutathione synthesis by the cyclopentenone prostaglandin, 15-deoxy-Delta12,14-prostaglandin J2. On exposure to 15-deoxy-Delta12,14-prostaglandin J2, the dissociation of Nrf2 from Keap1 occurred and this was dependent on the modification of thiols in Keap1. This mechanism appears to encompass other electrophilic lipids, since 15-A(2t)-isoprostane and the lipid aldehyde 4-hydroxynonenal were also shown to modify Keap1 and activate ARE. We propose that activation of ARE through this mechanism will have a major impact on inflammatory situations such as atherosclerosis, in which both enzymic as well as non-enzymic formation of electrophilic lipid oxidation products are increased.

An endogenous electrophile that modulates the regulatory mechanism of protein turnover: inhibitory effects of 15-deoxy-Delta 12,14-prostaglandin J2 on proteasome

Prostaglandin D(2) (PGD(2)), a major cyclooxygenase product in a variety of tissues and cells, readily undergoes dehydration to yield electrophilic PGs, such as 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)). We have previously shown that 15d-PGJ(2) potently induces apoptosis of SH-SY5Y human neuroblastoma cells via accumulation of the tumor suppressor gene product p53. In the study presented here, we investigated the molecular mechanisms involved in the 15d-PGJ(2)-induced accumulation of p53. It was observed that 15d-PGJ(2) potently induced p53 protein expression but scarcely induced p53 gene expression. In addition, exposure of the cells to 15d-PGJ(2) resulted in an accumulation of ubiquitinated proteins and in a significant inhibition of proteasome activities, suggesting that 15d-PGJ(2) acted on the ubiquitin-proteasome pathway, a regulatory mechanism of p53 turnover. The effects of 15d-PGJ(2) on the protein turnover were attributed to its electrophilic feature, based on the observations that (i) the reduction of the double bond in the cyclopentenone ring of 15d-PGJ(2) virtually abolished the effects on protein turnover, (ii) overexpression of an endogenous redox regulator, thioredoxin 1, significantly retarded the inhibition of proteasome activities and accumulations of p53 and ubiquitinated proteins induced by 15d-PGJ(2), and (iii) treatment of SH-SY5Y cells with biotinylated 15d-PGJ(2) indeed resulted in the formation of a 15d-PGJ(2)-proteasome conjugate. These data suggest that the modulation of proteasome activity may be involved in the mechanism responsible for the accumulation of p53 and subsequent induction of apoptotic cell death induced by 15d-PGJ(2).

Prostaglandins are powerful inducers of NGF and BDNF production in mouse astrocyte cultures

We found that prostaglandin (PG) D(2) and PGE(2), which are major PGs in the brain of mammals, powerfully induced the secretion of nerve growth factor (NGF) from cultured mouse astrocytes; PGE(2) or PGD(2) induced an approximately 12- or 19-fold increase in NGF secretion after a 24-h incubation, respectively. Moreover, it was found that the sequential metabolites of PGD(2), PGJ(2), Delta(12)-PGJ(2), and 15-deoxy-Delta(12,14)-PGJ(2), induced the NGF secretion to the culture medium strikingly (60-98-fold of the control after a 24-h incubation). NGF secretion induced by the J(2) series of PGs was accompanied by the increased expression of NGF mRNA. These PGs also stimulated the secretion/synthesis of brain-derived neurotrophic factor (BDNF). Our findings suggest that PGs play a neuroprotective role by inducing NGF and BDNF production in the central nervous system.

Thiol antioxidant and thiol-reducing agents attenuate 15-deoxy-Δ12,14-prostaglandin J2-induced heme oxygenase-1 expression

Heme oxygenase-1 (HO-1) is induced as a beneficial and adaptive response in cells and tissues exposed to oxidative stress. Herein we examined how various eicosanoids affect the induction of HO-1, and the possible mechanism underlying 15-deoxy-Delta(12,14)- prostaglandin J(2) (15d-PGJ(2))-induced HO-1 expression. PGH(2), PGD(2) and its metabolites of the PGJ(2) series, and PGA(1) markedly induced the protein expression of HO-1. Arachidonic acid (AA), docosahexaenoic acid (DHA), PGE(2), PGF(2 alpha), and thromboxane B(2) (TXB(2)) were shown to have no effect on the induction of HO-1. 15d-PGJ(2) was the most potent activator achieving significance at 5 microM. Although 15d-PGJ(2) significantly activated the MAPKs of JNK and ERK, the activation of JNK and ERK did not contribute to the induction of HO-1 as determined using transfection of dominant-negative plasmids and MAPKs inhibitors. Additional experiment indicated that 15d-PGJ(2) induced HO-1 expression through peroxisome proliferator-activated receptor (PPAR)-independent pathway. 15d-PGJ(2) significantly decreased the intracellular level of reduced glutathione; and the thiol antioxidant, N-acetyl-L-cysteine (NAC), and the thiol-reducing agent, dithiothreitol (DTT), inhibited the induction of HO-1 by 15d-PGJ(2). Finally, NAC and DTT exhibited significant inhibition of HO-1 mRNA and HO-1 promoter reporter activity induced by 15d-PGJ(2). These results suggest that thiol antioxidant and reducing agents attenuate the expression of HO-1 induced by 15d-PGJ(2), and that the cellular thiol-disulfide redox status may be linked to HO-1 activation.

Stress protein activation by the cyclopentenone prostaglandin 15-deoxy-Δ12,14-prostaglandin J2 in human mesangial cells

BACKGROUND

The cyclopentenone prostaglandin 15-deoxy-delta12,14-prostaglandin J2 (15dPGJ2) affects mesangial proliferation, survival and production of proinflammatory proteins. During a survey of the mesangial cell proteome after treatment with 15dPGJ2, heat shock protein 70 (HSP70) was found to be the most conspicuously up-regulated protein, suggesting that stress proteins are key mediators or modulators of the effects of 15dPGJ2. Because cyclopentenone prostaglandins are highly reactive toward intracellular thiols, the role of intracellular thiol modification in the stress response to 15dPGJ2 was examined.

METHODS

Human mesangial cells were treated with 15dPGJ2 and intracellular thiol status was monitored by the fluorescent thiol probe monobromobimane (MBB). Specific intracellular thiol pools were manipulated by treating the cells with buthionine sulfoximine (BSO) to deplete glutathione (GSH), or phenylarsine oxide (PAO) to modify protein vicinal dithiols. Transcription pathways were examined with reporter gene or adenoviral constructs.

RESULTS

15dPGJ2 decreased mesangial GSH and other intracellular thiols, but depletion of GSH specifically with BSO did not induce HSP70. Thiol-replenishing reagents, which can restore modified protein thiols, attenuated 15dPGJ2-induced HSP70 levels. Furthermore, PAO mimicked the effects of 15dPGJ2 on HSP70. 15dPGJ2 also activated the stress-responsive transcription factor Nrf2, which requires thiol modification of its cytoplasmic inhibitor protein for transcriptional activity, and induced the Nrf2-dependent stress protein heme oxygenase-1 (HO-1).

CONCLUSION

15dPGJ2 activates a stress response in human mesangial cells by covalent modification of protein thiols through its unique cyclopentenone ring structure. This stress response may be beneficial in preventing renal cell injury or death during kidney inflammation or ischemia.

Prostaglandin synthases: recent developments and a novel hypothesis

Cells are continuously exposed to cues, which signal cell survival or death. Fine-tuning of these conflicting signals is essential for tissue development and homeostasis, and defective pathways are linked to many disease processes, especially cancer. It is well established that prostaglandins (PGs), as signalling molecules, are important regulators of cell proliferation, differentiation and apoptosis. PG production has been a focus of many researchers interested in the mechanisms of parturition. Previously, investigators have focussed on the committed step of PG biosynthesis, the conversion by prostaglandin H synthase (PGHS; also termed cyclo-oxygenase, COX) of arachidonic acid (AA) (substrate) to PGH2, the common precursor for biosynthesis of the various prostanoids. However, recently the genes encoding the terminal synthase enzymes involved in converting PGH2 to each of the bioactive PGs, including the major uterotonic PGs, PGE2 (PGE synthase) and PGF2alpha (PGF synthase), have been cloned and characterized. This review highlights how the regulation of the expression and balance of key enzymes can produce, from a single precursor, prostanoids with varied and often opposing effects.

15d-PGJ2 inhibits oxidized LDL-induced macrophage proliferation by inhibition of GM-CSF production via inactivation of NF-κB

Macrophage-derived foam cells play an important role in atherosclerotic lesions. Oxidized low-density lipoprotein (Ox-LDL) induces macrophage proliferation via production of GM-CSF in vitro. This study investigated the effects of 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), a natural ligand for peroxisome proliferator-activated receptor gamma, on macrophage proliferation. Mouse peritoneal macrophages and RAW264.7 cells were used for proliferation study and reporter gene assay, respectively. Twenty microgram per milliliter of Ox-LDL induced [3H]thymidine incorporation in mouse peritoneal macrophages, and 15d-PGJ(2) inhibited Ox-LDL-induced [3H]thymidine incorporation in a dose-dependent manner. Ox-LDL increased GM-CSF release and GM-CSF mRNA expression, and activated GM-CSF gene promoter, all of which were prevented by 15d-PGJ(2) or 2-cyclopenten-1-one, a cyclopentenone ring of 15d-PGJ(2). The suppression of GM-CSF promoter activity by 15d-PGJ(2) and 2-cyclopenten-1-one was mediated through reduction of NF-kappaB binding to GM-CSF promoter. These results suggest that 15d-PGJ(2) inhibits Ox-LDL-induced macrophage proliferation through suppression of GM-CSF production via NF-kappaB inactivation.

15-Deoxy-Delta(12,14)-prostaglandin J2 induces apoptosis through activation of the CHOP gene in HeLa cells

Cyclopentenone prostaglandins (PGs) of the J series, which are produced by dehydration of PGD(2), have been reported to induce apoptosis in various cell lines. One of these cyclopentenone PGs, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-d-PGJ(2)), is the most potent inducer of apoptosis in the series, but the signaling pathways by which it induces apoptosis are poorly understood. We recently reported that cyclopentenone PGs accumulate in the endoplasmic reticulum (ER) and it has been shown that the transcription factor CHOP is induced by ER-stresses and elicits apoptosis. In the present study we demonstrated that 15-d-PGJ(2) induces CHOP mRNA/protein in HeLa cells via activation of the conserved regions in the CHOP promoter. Using several mutants of the CHOP promoter fragments, we found that two regions, CCAAT/enhancer-binding protein (C/EBP) site at -313 and ER-stress element (ERSE) at -93, are involved in activation of the CHOP gene by 15-d-PGJ(2). These results suggest that 15-d-PGJ(2) activates the CHOP promoter in two distinct pathways that could induce apoptosis of HeLa cells.

Transcription factor Nrf2 regulates inflammation by mediating the effect of 15-deoxy-Delta(12,14)-prostaglandin j(2)

Activated macrophages express high levels of Nrf2, a transcription factor that positively regulates the gene expression of antioxidant and detoxication enzymes. In this study, we examined how Nrf2 contributes to the anti-inflammatory process. As a model system of acute inflammation, we administered carrageenan to induce pleurisy and found that in Nrf2-deficient mice, tissue invasion by neutrophils persisted during inflammation and the recruitment of macrophages was delayed. Using an antibody against 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), it was observed that macrophages from pleural lavage accumulate 15d-PGJ(2). We show that in mouse peritoneal macrophages 15d-PGJ(2) can activate Nrf2 by forming adducts with Keap1, resulting in an Nrf2-dependent induction of heme oxygenase 1 and peroxiredoxin I (PrxI) gene expression. Administration of the cyclooxygenase 2 inhibitor NS-398 to mice with carrageenan-induced pleurisy caused persistence of neutrophil recruitment and, in macrophages, attenuated the 15d-PGJ(2) accumulation and PrxI expression. Administration of 15d-PGJ(2) into the pleural space of NS-398-treated wild-type mice largely counteracted both the decrease in PrxI and persistence of neutrophil recruitment. In contrast, these changes did not occur in the Nrf2-deficient mice. These results demonstrate that Nrf2 regulates the inflammation process downstream of 15d-PGJ(2) by orchestrating the recruitment of inflammatory cells and regulating the gene expression within those cells.

Thioredoxin as a molecular target of cyclopentenone prostaglandins

Prostaglandin (PG) D2, a major cyclooxygenase product in a variety of tissues and cells, readily undergoes dehydration to yield the bioactive cyclopentenone-type PGs of the J2 series, such as 15-deoxy-Delta12,14-PGJ2 (15d-PGJ2). We have shown previously that 15d-PGJ2 is a potent electrophile that causes intracellular oxidative stress and redox alteration in human neuroblastoma SH-SY5Y cells. In the present study, based on the observation that the electrophilic center of 15d-PGJ2 was involved in the pro-oxidant effect, we investigated the role of thioredoxin 1 (Trx), an endogenous redox regulator, against 15d-PGJ2-induced oxidative cell injury. It was observed that the 15d-PGJ2-induced oxidative stress was significantly suppressed by the Trx overexpression. In addition, the treatment of SH-SY5Y cells with biotinylated 15d-PGJ2 resulted in the formation of a 15d-PGJ2-Trx adduct, indicating that 15d-PGJ2 directly modified the endogenous Trx in the cells. To further examine the mechanism of the 15d-PGJ2 modification of Trx, human recombinant Trx treated with 15d-PGJ2 was analyzed by mass spectrometry. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis of the 15d-PGJ2-treated human recombinant Trx demonstrated the addition of one molecule of 15d-PGJ2 per protein molecule. Moreover, the electrospray ionization-liquid chromatography/mass spectrometry/mass spectrometry analysis identified two cysteine residues, Cys-35 and Cys-69, as the targets of 15d-PGJ2. These residues may represent the direct sensors of the electrophilic PGs that induce the intracellular redox alteration and neuronal cell death.

Role of heme oxygenase-1 protein in the neuroprotective effects of cyclopentenone prostaglandin derivatives under oxidative stress

Previously we found that some cyclopenteone prostaglandin derivatives (PGs), referred to as neurite outgrowth-promoting PGs (NEPPs), have dual biological activities of promoting neurite outgrowth and preventing neuronal death [Satoh et al. (2000) J. Neurochem., 75, 1092-1102; Satoh et al. (2001) J. Neurochem., 77, 50-62; Satoh et al. (2002) In Kikuchi, II. (ed.), Strategenic Medical Science Against Brain Attack. Springer-Verlag, Tokyo, pp. 78-93]. To investigate possible cellular mechanisms of the neuroprotective effects, we performed oligo hybridization-based DNA array analysis with mRNA isolated from HT22, a cell line that originated from a mouse hippocampal neuron. Several transcripts up-regulated by NEPP11 were identified. Because heme oxygenase 1 (HO-1) mRNA was the most prominently induced and was earlier reported to protect neuronal and non-neuronal cells against oxidative stress, we focused on it as a possible candidate responsible for the neuroprotective effects. We found NEPP11 to induce HO-1 protein (32 kDa) in HT22 cells in both the presence and the absence of glutamate, whereas non-neuroprotective prostaglandins (PGs) Delta12-PGJ2 or PGA2 did not. Overexpression of HO-1-green fluorescence protein (GFP) fusion protein significantly protected HT22 cells against oxidative glutamate toxicity, whereas that of GFP alone did not. Furthermore, biliverdin and bilirubin, products of HO-1 enzymatic activity on heme, protected HT22 cells from oxidative glutamate toxicity. These results, together with our previous results, suggest that NEPP11 activates the expression of HO-1 and that HO-1 produces biliverdin and bilirubin, which result in the inhibition of neuronal death induced by oxidative stress. NEPP11 is the first molecular probe reported to have a neuroprotective action through induction of HO-1 in neuronal cells.

Involvement of c-jun N-terminal kinase activation in 15-deoxy-delta12,14-prostaglandin J2-and prostaglandin A1-induced apoptosis in AGS gastric epithelial cells

Cyclopentenone prostaglandins (CyPGs), derivatives of arachidonic acid, have been suggested to exert growth-inhibitory activity through peroxisome proliferator-activated receptor (PPAR)-dependent and -independent mechanisms. Here we examined various eicosanoids for growth inhibition and found that the terminal derivative of prostaglandin (PG) J(2) metabolism, 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), and PGA(1) markedly inhibited the growth and induced apoptosis in AGS gastric carcinoma cells. There were no significant increases in cell death and DNA-fragmentation in the cells with overexpression of PPARalpha or PPARgamma, indicating the possibility that 15d-PGJ(2) and PGA(1) induced apoptosis through PPAR-independent pathway. Moreover, 15d-PGJ(2) and PGA(1) activated the c-jun N-terminal kinase (JNK) and caspase-3 activity in dose- and time-dependent manners. To examine further the role of JNK signaling cascades in apoptosis induced by 15d-PGJ(2) and PGA(1), we transfected dominant-negative (DN) mutants of JNK plasmid into the cells to analyze the apoptotic characteristics of cells overexpressing DN-JNK following exposure to 15d-PGJ(2) and PGA(1). Overexpression of DN-JNK significantly repressed both endogenous JNK and caspase-3 activity, and subsequently decreased apoptosis induced by 15d-PGJ(2) and PGA(1). These results suggested that CyPGs, such as 15d-PGJ(2) and PGA(1), activated JNK signaling pathway, and that JNK activation may be involved in 15d-PGJ(2)- and PGA(1)-induced apoptosis.

Peroxisome proliferator-activated receptors: a critical review on endogenous pathways for ligand generation

Lipid mediators can exert their effects by interactions with well-characterised cell surface G-protein-linked receptors. Recently, a group of intracellular receptors have been identified that are activated by a large variety of lipid-derived mediators. Amongst these novel targets, the peroxisome proliferator-activated receptors (PPARs), a family of three (PPARalpha, beta/delta and gamma) nuclear receptor/transcription factors have become a major area for investigation. PPARs are found throughout the body, where they have diverse roles regulating lipid homeostasis, cellular differentiation, proliferation and the immune response. There is a great interest, therefore, in the roles of PPARs in a variety of pathological conditions, including diabetes, atherosclerosis, cancer and chronic inflammation. Although, a number of naturally occurring compounds can activate PPARs, it has been difficult, as yet, to characterise any of these mediators as truly endogenous ligands. These findings have lead to the suggestion that PPARs may act just as general lipid sensors. Acting as lipid sensors, PPARs may take changes in lipid/fatty acid balance in the diet or local metabolism and translate them to tissue-specific ligands, exerting tissue-specific effects. Using classical pharmacological criteria for endogenous mediator classification we will critically discuss the variety of pathways for putative ligand generation.

Cytokines, prostaglandins and parturition--a review

The elaboration of cytokines, chemokines and immunomodulatory proteins in the placenta and gestational membranes has been extensively investigated in the context of both normal and abnormal pregnancy and delivery. Patterns of expression of cytokines in the foetal membranes and decidua suggest that inflammatory activation occurs modestly with term labour, but much more robustly in preterm delivery, particularly in the presence of intrauterine infection. Enhanced chemokine expression, particularly evident in deliveries with an infected amniotic cavity, is presumably responsible for recruiting infiltrating leukocytes into the membranes thereby amplifying the inflammatory process and hastening membrane rupture and delivery. Anti-inflammatory cytokines suppress inflammatory reactions in the placenta, but under some circumstances may act in a pro-inflammatory fashion in the membranes. Intracellular signalling by cytokines is modulated by proteins such as SOCS (Silencer Of Cytokine Signalling)-1, -2 and -3. Changes in the abundance of these proteins occur with term labour, implicating them as modulators of cytokine actions around the time of parturition. Prostaglandins, released by the membranes in response to stretch and the actions of pro-inflammatory cytokines, act not only upon the myometrium and cervix, but may also exert paracrine/autocrine effects on cell viability and matrix protein integrity. The localization and regulation of prostanoid isomerases, responsible for converting PGH(2) (derived from prostaglandin H synthase-1 and -2) to bioactive prostanoids, are being studied in these tissues, particularly in the context of cytokine interactions. Although the gestational tissues are known to be sources of PGD(2), PGJ(2) and its derivatives, the regulation of production of these prostaglandins has yet to be studied in any detail and their actions, which may include apoptosis and suppression of inflammation, remain poorly defined. A more complete understanding of these aspects of cytokine-prostaglandin interactions in pregnancy and parturition will, no doubt, unfold as current studies come to fruition.

Activation of p38 mitogen-activated protein kinase and activator protein-1 during the promotion of neurite extension of PC-12 cells by 15-deoxy-delta12,14-prostaglandin J2

15-Deoxy-Delta(12,14)-prostaglandin J(2) (15-deoxy-PGJ(2)), a naturally occurring ligand, activates the peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Activation of PPAR-gamma has been found to induce cell differentiation in such cells as adipose cells and macrophages. Herein, we investigated whether 15-deoxy-PGJ(2) has neuronal cell differentiation and possible underlying molecular mechanisms. Dopaminergic differentiating PC-12 cells treated with 15-deoxy-PGJ(2) (0.2 to 1.6 microM) alone showed measurable neurite extension and expression of neurofilament, a marker of cell differentiation. However, a much greater extent of neurite extension and expression of neurofilament was observed in the presence of NGF (50 ng/ml). In parallel with its increasing effect on the neurite extension and expression of neurofilament, 15-deoxy-PGJ(2) enhanced NGF-induced p38 MAP kinase expression and its phosphorylation in addition to the activation of transcription factor AP-1 in a dose-dependent manner. Moreover, pretreatment of 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(pyridyl)1H-imidazole (SB203580), a specific inhibitor of p38 MAP kinase, inhibited the promoting effect of 15-deoxy-PGJ(2) (0.8 microM) on NGF-induced neurite extension. This inhibition correlated well with the ability of SB203580 to inhibit the enhancing effect of 15-deoxy-PGJ(2) on the expression of p38 MAP kinase and activation of AP-1. The promoting ability of 15-deoxy-PGJ(2) did not occur through PPAR-gamma because synthetic PPAR-gamma agonist and antagonist did not change the neurite-promoting effect of 15-deoxy-PGJ(2). In addition, contrast to other cells (embryonic midbrain and neuroblastoma SK-N-MC cells), PPAR-gamma was not expressed in PC-12 cells. Other structure-related prostaglandins (PGD(2) and PGE(2)) acting via a cell surface G-protein-coupled receptor (GPCR) did not increase basal or NGF-induced neurite extension. Moreover, GPCR (PGE(2) and PGD(2) receptors) antagonists did not alter the promoting effect of 15-deoxy-PGJ(2) on neurite extension and activation of p38 MAP kinase, suggesting that the promoting effect of 15-deoxy-PGJ(2) may not be mediated by GPCR either. These data demonstrate that activation of p38 MAP kinase in conjunction with AP-1 signal pathway may be important in the promoting activity of 15-deoxy-PGJ(2) on the differentiation of PC-12 cells.

[Neurotrophin-like low molecular weight compounds]

A large number of compounds have been reported to prevent ischemia-induced neuronal death, whereas there are few described to enhance recovery of brain functions. Since neurotrophins do not only prevent neuronal death but also protect neuronal circuits, they may be potential candidates. However, their poor penetration of the blood-brain-barrier hampers their development as therapeutic agents. In this context, low-molecular-weight compounds that possess neurite outgrowth- and neuronal survival-promoting activities may be alternative candidates. Neurite outgrowth-promoting prostaglandins, which were recently-synthesized based on the chemical structure of anti-tumor cyclopentenone prostaglandin derivatives, have been characterized by their neurotrophic effects on neurons in the central nervous system. In this paper, we present a review of these compounds as therapeutic agents against several neurodegenerative diseases.

Formation of highly reactive A-ring and J-ring isoprostane-like compounds (A4/J4-neuroprostanes) in vivo from docosahexaenoic acid

Free radical-initiated oxidant injury and lipid peroxidation have been implicated in a number of neural disorders. Docosahexaenoic acid is the most abundant unsaturated fatty acid in the central nervous system. We have shown previously that this 22-carbon fatty acid can yield, upon oxidation, isoprostane-like compounds termed neuroprostanes, with E/D-type prostane rings (E(4)/D(4)-neuroprostanes). Eicosanoids with E/D-type prostane rings are unstable and dehydrate to cyclopentenone-containing compounds possessing A-type and J-type prostane rings, respectively. We thus explored whether cyclopentenone neuroprostanes (A(4)/J(4)-neuroprostanes) are formed from the dehydration of E(4)/D(4)-neuroprostanes. Indeed, oxidation of docosahexaenoic acid in vitro increased levels of putative A(4)/J(4)-neuroprostanes 64-fold from 88 +/- 43 to 5463 +/- 2579 ng/mg docosahexaenoic acid. Chemical approaches and liquid chromatography/electrospray ionization tandem mass spectrometry definitively identified them as A(4)/J(4)-neuroprostanes. We subsequently showed these compounds are formed in significant amounts from a biological source, rat brain synaptosomes. A(4)/J(4)-neuroprostanes increased 13-fold, from a basal level of 89 +/- 72 ng/mg protein to 1187 +/- 217 ng/mg (n = 4), upon oxidation. We also detected these compounds in very large amounts in fresh brain tissue from rats at levels of 97 +/- 25 ng/g brain tissue (n = 3) and from humans at levels of 98 +/- 26 ng/g brain tissue (n = 5), quantities that are nearly an order of magnitude higher than other classes of neuroprostanes. Because of the fact that A(4)/J(4)-neuroprostanes contain highly reactive cyclopentenone ring structures, it would be predicted that they readily undergo Michael addition with glutathione and adduct covalently to proteins. Indeed, incubation of A(4)/J(4)-neuroprostanes in vitro with excess glutathione resulted in the formation of large amounts of adducts. Thus, these studies have identified novel, highly reactive A/J-ring isoprostane-like compounds that are derived from docosahexaenoic acid in vivo.

Induction of cellular oxidative stress by aryl hydrocarbon receptor activation

The aryl hydrocarbon receptor (AHR) has long been associated with the induction of a battery of genes involved in the metabolism of foreign and endogenous compounds. Depending on experimental conditions, AHR can mediate either activation or amelioration of chemical toxicity. For the past decade, evidence has mounted that AHR is associated with a cellular oxidative stress response that must be considered when evaluating the mechanism of action of xenobiotics capable of activating AHR, or capable of metabolic activation by enzymes encoded by genes under control of AHR. In this review, we have evaluated the diverse mechanisms by which AHR generates an oxidative stress response, including inflammation, antioxidant and prooxidant enzymes and cytochrome P450. A review of the regulation of Ahr transcription and functional polymorphisms especially related to oxidative stress is also included. We have carefully avoided placing a value judgment on the degree of toxicity produced by such a response, in view of the realization that an oxidative response is involved in many normal physiological processes. Since the interface between physiological, adaptive and toxicological responses elicited by the AHR-mediated oxidative stress response is not clearly defined, it behooves the researcher to evaluate both toxicological and physiological features of the response.

Human colorectal cancer cells efficiently conjugate the cyclopentenone prostaglandin, prostaglandin J(2), to glutathione

Cyclopentenone prostaglandins (PGs), particularly those of the J-series, affect proliferation and differentiation in a number of cell lines. J-ring PGs have been shown to be ligands for the peroxisome proliferator-activated receptor (PPAR)-gamma and to modulate NF-kappaB-mediated gene transcription. We have previously reported that large quantities of eicosanoids, including PGJ(2), are produced by the human colorectal cancer cell line HCA-7 while lesser amounts of Delta(12)-PGJ(2) and 15-deoxy-Delta(12,14)-PGJ(2) are formed. In this and other cell lines, cyclopentenone PGs have been shown to increase cell proliferation, but factors that influence their formation and metabolism are poorly understood. Unlike other PGs, cyclopentenone PGs contain alpha,beta-unsaturated carbonyl groups that readily adduct various biomolecules such as glutathione (GSH) in vitro. We now report that in HCA-7 cells, PGJ(2) is largely metabolized by conjugation to GSH. Characterization of the adducts by liquid chromatography (LC)-mass spectrometry (MS) revealed two major metabolites consisting of (1) a novel GSH conjugate in which the carbonyl at C-11 of PGJ(2) is reduced and (2) intact PGJ(2) conjugated to GSH. Approximately 70% of the PGJ(2) added to HCA-7 cells was esterifed to GSH after 2 h of incubation, suggesting this pathway represents the major route of metabolic disposition of PGJ(2) in HCA-7 cells.

Cyclopentenone prostaglandin receptors

Cyclopentenone prostaglandins (PGs), such as 15-deoxy-12,13-didehydro-14,15-didehydro-PGJ2 (15d-delta(12,14)-PDJ2), 12,13-didehydro-PGJ2 (delta12-PGJ2) and PGA2, are actively transported into cells and promote the expression of a variety of genes. The ultimate metabolite of PGD2, 15d-delta(12,14)-PGJ2, specifically binds to a nuclear receptor, the gamma isoform of the peroxisome proliferator-activated receptor, thereby promoting adipogenesis. Cyclopentenone PGs also induce the expression of various stress genes, such as heat shock proteins (HSPs), the immunoglobulin heavy chain binding protein (BiP) and protein disulfide isomerase by acting through heat shock element or unfolded protein response element. Overall, cyclopentenone PGs regulate cell growth, cell differentiation and stress responses by regulating various gene expression.

Prostaglandin D2 and its metabolites induce caspase-dependent granulocyte apoptosis that is mediated via inhibition of I kappa B alpha degradation using a peroxisome proliferator-activated receptor-gamma-independent mechanism

Many inflammatory mediators retard granulocyte apoptosis. Most natural PGs studied herein (e.g., PGE(2), PGA(2), PGA(1), PGF(2 alpha)) either delayed apoptosis or had no effect, whereas PGD(2) and its metabolite PGJ(2) selectively induced eosinophil, but not neutrophil apoptosis. This novel proapoptotic effect does not appear to be mediated via classical PG receptor ligation or by elevation of intracellular cAMP or Ca(2+). Intriguingly, the sequential metabolites Delta(12)PGJ(2) and 15-deoxy-Delta(12,) Delta(14)-PGJ(2) (15dPGJ(2)) induced caspase-dependent apoptosis in both granulocytes, an effect that did not involve de novo protein synthesis. Despite the fact that Delta(12)PGJ(2) and 15dPGJ(2) are peroxisome proliferator-activated receptor-gamma (PPAR-gamma) activators, apoptosis was not mimicked by synthetic PPAR-gamma and PPAR-alpha ligands or blocked by an irreversible PPAR-gamma antagonist. Furthermore, Delta(12)PGJ(2) and 15dPGJ(2) inhibited LPS-induced I kappa B alpha degradation and subsequent inhibition of neutrophil apoptosis, suggesting that apoptosis is mediated via PPAR-gamma-independent inhibition of NF-kappa B activation. In addition, we show that TNF-alpha-mediated loss of cytoplasmic I kappa B alpha in eosinophils is inhibited by 15dPGJ(2) in a concentration-dependent manner. The selective induction of eosinophil apoptosis by PGD(2) and PGJ(2) may help define novel therapeutic pathways in diseases in which it would be desirable to specifically remove eosinophils but retain neutrophils for antibacterial host defense. The powerful proapoptotic effects of Delta(12)PGJ(2) and 15dPGJ(2) in both granulocyte types suggest that these natural products control the longevity of key inflammatory cells and may be relevant to understanding the control and resolution of inflammation.

PPARgamma ligands suppress proliferation of human urothelial basal cells in vitro

Expression of peroxisome proliferator-activated receptor (PPAR) gamma in the human urinary tract through embryonic development suggests its possible roles in the development, proliferation, and differentiation of uroepithelium. Little is known, however, about physiological roles of PPARgamma in the urinary tract. We investigated effects of PPARgamma ligands on the proliferation of normal human urothelial cells and stromal cells cultivated from surgical specimens. Active proliferation in vitro as well as high molecular weight cytokeratin expression indicated that cultured urothelial cells possess basal cell phenotype. PPARgamma protein, expressed predominantly in the epithelial layer of the normal human urinary tract in vivo, was abundantly expressed in urothelial cells but barely detectable in stromal cells in vitro. Natural ligand for PPARgamma, 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)), as well as synthetic ones, troglitazone and pioglitazone, suppressed proliferation of the urothelial cells dose-dependently. These effects were PPARgamma specific because clofibrate or PGF(2alpha) did not affect proliferation of urothelial cells. Neither 9-cis retinoic acid or all-trans retinoic acid (ATRA) at 1 microM showed any synergism on the antiproliferative effects of PPARgamma ligands. Urothelial cells treated with PPARgamma ligands showed drastic morphologic changes and cell cycle arrest at G0/G1 phase accompanied with increased mRNA level of a cyclin-dependent kinase inhibitor p21(WAF1/CIP1). Since 15d-PGJ(2) is present in vivo during the resolution phase of inflammation, these results indicated that PPARgamma might be involved in the terminal phase of urothelial re-epithelialization processes.

15-Deoxy-Delta12,14-prostaglandin J2 inhibits IL-1beta-induced cyclooxygenase-2 expression in mesangial cells

BACKGROUND

Cyclooxygenase-2 (COX-2), a key enzyme in the synthesis of prostaglandins, is induced in mesangial cells in response to proinflammatory cytokines. Recently, 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2), one of the natural ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), has been reported to have an anti-inflammatory effect. Therefore, we examined the effect of 15d-PGJ2 on COX-2 expression in cultured rat mesangial cells.

METHODS

Mesangial cells were incubated with 15d-PGJ2 for 30 minutes and then exposed to interleukin-1beta (IL-1beta). The expression of COX-2 mRNA and proteins was determined by Northern blot and immunoblot analyses, respectively. Accumulation of prostaglandin E2 (PGE2) was measured by an enzyme-linked immunosorbent assay (ELISA). Activities of mitogen-activated protein kinases (MAPKs) were evaluated by an immunoblot analysis. DNA binding activities of activator protein-1 (AP-1) or nuclear factor-kappaB (NF-kappaB) were examined by an electrophoretic mobility shift assay (EMSA). The activities of PPAR responsive elements (PPRE) and COX-2 promoter were measured by a luciferase reporter assay.

RESULTS

15D-PGJ2 significantly suppressed IL-1beta-induced COX-2 expression and PGE2 production, but thiazolidinediones, synthetic PPARgamma ligands, did not affect COX-2 expression. Moreover, the cells transfected with a PPRE luciferase reporter did not respond to 15d-PGJ2. IL-1beta rapidly activated extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK), which were involved in the up-regulation of COX-2 induction, but 15d-PGJ2 inhibited the activation of these kinases. 15d-PGJ2 inhibited the IL-1beta-induced increase in binding activities of nuclear proteins to consensus AP-1 site and AP-1-like site of COX-2 promoter but not of NF-kappaB. IL-1beta was unable to activate the COX-2 promoter when the AP-1-like site was mutated.

CONCLUSIONS

These data suggest that 15d-PGJ2 inhibits IL-1beta-induced COX-2 expression, independent of PPARgamma activation, by suppression of ERK and JNK pathways and AP-1 activation in mesangial cells. Thus, 15d-PGJ2 may play an important role in the negative feedback mechanism of COX-2 expression in renal inflammation and may be useful as an anti-inflammatory agent.

15-Deoxy-Delta(12,14)-prostaglandin J(2): the endogenous electrophile that induces neuronal apoptosis

Prostaglandin D(2) (PGD(2)), a major cyclooxygenase product in a variety of tissues and cells, readily undergoes dehydration to yield the bioactive cyclopentenone-type PGs of the J(2)-series, such as 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)). The observation that the level of 15d-PGJ(2) increased in the tissue cells from patients with sporadic amyotrophic lateral sclerosis suggested that the formation of 15d-PGJ(2) may be closely associated with neuronal cell death during chronic inflammatory processes. In vitro experiments using SH-SY5Y human neuroblastoma cells revealed that 15d-PGJ(2) induced apoptotic cell death. An oligonucleotide microarray analysis demonstrated that, in addition to the heat shock-responsive and redox-responsive genes, the p53-responsive genes, such as gadd45, cyclin G1, and cathepsin D, were significantly up-regulated in the cells treated with 15d-PGJ(2). Indeed, the 15d-PGJ(2) induced accumulation and phosphorylation of p53, which was accompanied by a preferential redistribution of the p53 protein in the nuclei of the cells and by a time-dependent increase in p53 DNA binding activity, suggesting that p53 accumulated in response to the treatment with 15d-PGJ(2) was functional. The 15d-PGJ(2)-induced accumulation of p53 resulted in the activation of a death-inducing caspase cascade mediated by Fas and the Fas ligand.

15-Deoxy-Delta12,14-prostaglandin J2 regulates mesangial cell proliferation and death

BACKGROUND

Proliferation of intrinsic glomerular cells is a common response to renal injury. Acutely, proliferation may be beneficial, but sustained glomerular hypercellularity after injury is associated with progressive renal failure. To identify endogenous factors that may be responsible for regulating glomerular cell number, the effects of J-series cyclopentenone prostaglandins (PGs) on human glomerular mesangial cell proliferation and death were examined.

METHODS

Human mesangial cells were grown in the presence or absence of PGJ2 or its metabolite 15-Deoxy-Delta12,14-PGJ2 (15dPGJ2). The number of viable cells was measured by the reduction of the tetrazolium MTS to a colored formazan product. Apoptosis was assessed by caspase-3 activation and DNA fragmentation.

RESULTS

PGJ2 at concentrations up to 10 micromol/L caused mesangial proliferation. 15dPGJ2 also caused mesangial proliferation at low concentrations (< or =2.5 micromol/L), but induced mesangial cell death at higher concentrations (>5 micromol/L). Cell death occurred in part through apoptosis, measured as an increase in caspase-3 activity and DNA fragmentation in 15dPGJ2-treated cells. Cell death was associated with a decline in baseline phosphorylation of the survival factor Akt and increased Akt degradation, whereas 15dPGJ2-induced mesangial proliferation was blocked by inhibition of the PI 3-kinase/Akt pathway. 15dPGJ2 is a potent PPARgamma agonist. Like 15dPGJ2, treatment of mesangial cells with thiazolidinedione-type PPARgamma ligands (10 to 20 micromol/L) caused significant cell death, but at lower concentrations also caused a small degree of proliferation.

CONCLUSIONS

J-series prostaglandins thus may be involved in the initiation of glomerular hypercellularity through Akt-dependent proliferation, and restoration of normal glomerular architecture through PPARgamma-mediated apoptosis. Manipulation of these prostaglandins may be relevant to the treatment of progressive glomerular disease.

Activation of the mouse heme oxygenase-1 gene by 15-deoxy-Delta(12,14)-prostaglandin J(2) is mediated by the stress response elements and transcription factor Nrf2

The mechanism of heme oxygenase-1 (ho-1) gene activation by 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) was examined. 15d-PGJ(2) stimulated expression of HO-1 mRNA and protein and of a mouse ho-1 gene promoter/luciferase fusion construct (HO15luc) in a dose-dependent manner in mouse hepatoma (Hepa) cells. HO15luc expression was not effected by troglitazone, a peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligand, but induction by 15d-PGJ(2) was abrogated by the antioxidant N-acetylcysteine. The primary 15d-PGJ(2) responsive sequences were localized to a 5' distal enhancer (E1) and identified as the stress-response element, previously shown to mediate ho-1 activation by several agents, including heme and heavy metals. Treatment of Hepa cells with 15d-PGJ(2) stimulated stress-response element-binding activity as judged by electrophoretic mobility shift assays. Antibody "supershift" experiments identified NF-E2 related factor 2 (Nrf2), but not Fos, Jun, or activating transcription factor/cyclic AMP response element binding protein transcription factors, within the 15d-PGJ(2)-induced complexes. Similarly, a dominant-negative mutant of Nrf2, but not of c-Jun or c-Fos, abrogated 15d-PGJ(2)-stimulated E1 transcription activity. Finally, prior induction of HO-1 in RAW264.7 mouse macrophages by 15d-PGJ(2) attenuated cell death caused by diesel exhaust particle extracts. These results demonstrate that induction of mouse HO-1 expression by 15d-PGJ(2) is independent of PPAR-gamma but dependent on oxidative stress, is regulated by the oxidative stress-activated transcription factor Nrf2, and provides cytoprotective activity.

Human B lymphocytes and B lymphomas express PPAR-gamma and are killed by PPAR-gamma agonists

This paper evaluates the expression and functional significance of PPAR-gamma on human B cells. Recent interest in PPAR-gamma has focused on its adipogenic effects on non-bone marrow-derived cells. PPAR-gamma agonists also have been proposed as anti-inflammatory agents owing to inhibition of NF-kappa B activation. We report herein the first study evaluating PPAR-gamma expression and functional significance in human B lineage cells. Interestingly, normal human B cells and a variety of B lymphoma cells (e.g., Daudi, Ramos, and Raji) express PPAR-gamma protein as determined by immunocytochemistry. The expression of 80-kDa PPAR-gamma on human B lymphocytes and B lymphomas was confirmed by Western blot analysis. 15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), a natural PPAR-gamma agonist, has a dose-dependent antiproliferative and cytotoxic effect on normal and malignant B cells as shown by [(3)H]thymidine and MTT assays. Only PPAR-gamma agonists (thiazolidinediones) and not PPAR-alpha agonists mimicked the effect of 15d-PGJ(2) on B lineage cells, indicating that the mechanism by which 15d-PGJ(2) negatively affects B lineage cells involves, in part, PPAR-gamma. The mechanism whereby PPAR-gamma agonists induce cytotoxicity is via apoptosis as shown by Annexin V staining and as confirmed by DNA fragmentation detected using the TUNEL assay. This is the first study evaluating PPAR-gamma expression and its significance on human B lymphocytes. PPAR-gamma agonists may serve as a counterbalance to the stimulating effects of other prostaglandins, namely PGE(2), which promotes B cell immunoglobulin class switching. Finally, the use of prostaglandins such as 15d-PGJ(2) and synthetic PPAR-gamma agonists to induce apoptosis in B lineage cells may lead to the development of novel therapies for potentially fatal B lymphomas.

15-deoxy-delta 12,14-prostaglandin J2. A prostaglandin D2 metabolite generated during inflammatory processes

Prostaglandin D(2) (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)), which have been suggested to exert anti-inflammatory effects in vivo. Meanwhile, the mechanism of these effects is not well understood and the natural site and the extent of its production in vivo remain unclear. In the present study, we raised a monoclonal antibody specific to 15d-PGJ(2) and determined its production in inflammation-related events. The monoclonal antibody (mAb11G2) was raised against the 15d-PGJ(2)-keyhole limpet hemocyanin conjugate and was found to recognize free 15d-PGJ(2) specifically. The presence of 15d-PGJ(2) in vivo was immunohistochemically verified in the cytoplasm of most of the foamy macrophages in human atherosclerotic plaques. In addition, the immunostaining of lipopolysaccharide-stimulated RAW264.7 macrophages with mAb11G2 demonstrated an enhanced intracellular accumulation of 15d-PGJ(2), suggesting that the PGD(2) metabolic pathway, generating the anti-inflammatory PGs, is indeed utilized in the cells during inflammation. The activation of macrophages also resulted in the extracellular production of PGD(2), which was associated with a significant increase in the extracellular 15d-PGJ(2) levels, and the extracellular 15d-PGJ(2) production was reproduced by incubating PGD(2) in a cell-free medium and in phosphate-buffered saline. Moreover, using a chiral high performance liquid chromatography method for separation of PGD(2) metabolites, we established a novel metabolic pathway, in which PGD(2) is converted to 15d-PGJ(2) via an albumin-independent mechanism.

Biphasic effects of 15-deoxy-delta(12,14)-prostaglandin J(2) on glutathione induction and apoptosis in human endothelial cells

The lipid products derived from the cyclooxygenase pathway can have diverse and often contrasting effects on vascular cell function. Cyclopentenone prostaglandins (cyPGs), such as 15-deoxy-Delta(12,14)-prostaglandin-J(2) (15d-PGJ(2)), a peroxisome proliferator-activated receptor-gamma (PPARgamma) agonist, have been reported to cause endothelial cell apoptosis, yet in other cell types, cyPGs induce cytoprotective mediators, such as heat shock proteins, heme oxygenase-1, and glutathione (GSH). Herein, we show in human endothelial cells that low micromolar concentrations of 15d-PGJ(2) enhance GSH-dependent cytoprotection through the upregulation of glutamate-cysteine ligase, the rate-limiting enzyme of GSH synthesis, as well as GSH reductase. The effect of 15d-PGJ(2) on GSH synthesis is attributable to the cyPG structure but is independent of PPAR, inasmuch as the other cyPGs, but not PPARgamma or PPARalpha agonists, are able to increase GSH. The increase in cellular GSH is accompanied by abrogation of the proapoptotic effects of 4-hydroxynonenal, a product of lipid peroxidation present in atherosclerotic lesions. However, higher concentrations of 15d-PGJ(2) (10 micromol/L) cause endothelial cell apoptosis, which is further enhanced by depletion of cellular GSH by buthionine sulfoximine. We propose that the GSH-dependent cytoprotective pathways induced by 15d-PGJ(2) contribute to its antiatherogenic effects and that these pathways are distinct from those leading to apoptosis.

PPAR gamma/RXR alpha heterodimers are involved in human CG beta synthesis and human trophoblast differentiation

Recent studies performed with null mice suggested a role of either RXR alpha or PPAR gamma in murine placental development. We report here that both PPAR gamma and RXR alpha are strongly expressed in human villous cytotrophoblasts and syncytiotrophoblasts. Moreover, specific ligands for RXRs or PPAR gamma (but not for PPAR alpha or PPAR delta) increase both human CG beta transcript levels and the secretion of human CG and its free beta-subunit. When combined, these ligands have an additive effect on human CG secretion. Pan-RXR and PPAR gamma ligands also have an additive effect on the synthesis of other syncytiotrophoblast hormones such as human placental lactogen, human placental GH, and leptin. Therefore, in human placenta, PPAR gamma/RXR alpha heterodimers are functional units during cytotrophoblast differentiation into the syncytiotrophoblast in vitro. Elements located in the regulatory region of the human CG beta gene (beta 5) were found to bind RXR alpha and PPAR gamma from human cytotrophoblast nuclear extracts, suggesting that PPAR gamma/RXR alpha heterodimers directly regulate human CG beta transcription. Altogether, these data show that PPAR gamma/RXR alpha heterodimers play an important role in human placental development.

Cyclopentenone prostaglandins inhibit cytokine-induced nf-kappab activation and chemokine production by human mesangial cells

In the kidney an uncontrolled inflammatory response to an acute insult may lead to chronic inflammation, permanent tissue damage, and progressive renal insufficiency. Resolution of acute inflammation likely is dependent on endogenous regulatory mechanisms activated in parallel with mediators of renal inflammation. These mechanisms are postulated to attenuate the renal expression of proinflammatory cytokines, including the chemokines responsible for recruiting leukocytes to the kidney, thus facilitating the transition from inflammation to healing. To understand the regulation of the inflammatory response within the kidney, the effects of anti-inflammatory J series cyclopentenone prostaglandins on chemokine production by human mesangial cells were examined. Treatment of mesangial cells with prostaglandin J(2) and 15-deoxy-Delta(12,14)-prostaglandin J(2) blocked interleukin-1beta-induced monocyte chemoattractant protein-1 mRNA expression and protein production. This correlated with failure of the transcription factor nuclear factor-kappaB (NF-kappaB) to translocate to the nucleus and bind to its recognition motif, a step required for cytokine-induced monocyte chemoattractant protein-1 gene activation. NF-kappaB failed to translocate because the cyclopentenone prostaglandins attenuated degradation of the NF-kappaB inhibitor IkappaB-alpha. These data suggest that certain prostaglandins can limit the extent of renal chemokine expression and thus may have an important role in resolving renal inflammation.

Cyclopentenone prostaglandins as potential inducers of intracellular oxidative stress

In the present study, we find that cyclopentenone prostaglandins (PGs) of the J(2) series, naturally occurring derivatives of PGD(2), are potential inducers of intracellular oxidative stress that mediates cell degeneration. Based on an extensive screening of diverse chemical agents on induction of intracellular production of reactive oxygen species (ROS), we found that the cyclopentenone PGs, such as PGA(2), PGJ(2), Delta(12)-PGJ(2), and 15-deoxy-Delta(12,14)-PGJ(2), showed the most potent pro-oxidant effect on SH-SY5Y human neuroblastoma cells. As the intracellular events that mediate the PG cytotoxicity, we observed (i) the cellular redox alteration represented by depletion of antioxidant defenses, such as glutathione and glutathione peroxidase; (ii) a transient decrease in the mitochondrial membrane potential (Deltapsi); (iii) the production of protein-bound lipid peroxidation products, such as acrolein and 4-hydroxy-2-nonenal; and (iv) the accumulation of ubiquitinated proteins. These events correlated well with the reduction in cell viability. In addition, the thiol compound, N-acetylcysteine, could significantly inhibit the PG-induced ROS production, thereby preventing cytotoxicity, suggesting that the redox alteration is closely related to the pro-oxidant effect of cyclopentenone PGs. More strikingly, the lipid peroxidation end products, acrolein and 4-hydroxy-2-nonenal, detected in the PG-treated cells potently induced the ROS production, which was accompanied by the accumulation of ubiquitinated proteins and cell death, suggesting that the membrane lipid peroxidation products may represent one of the causative factors that potentiate the cytotoxic effect of cyclopentenone PGs by accelerating intracellular oxidative stress. These data suggest that the intracellular oxidative stress, represented by ROS production/lipid peroxidation and redox alteration, may underlie the well documented biological effects, such as antiproliferative and antitumor activities, of cyclopentenone PGs.

Binding of prostaglandins to human PPARgamma: tool assessment and new natural ligands

The peroxisome proliferator-activated receptors (PPAR) form a family of nuclear receptors with a wide variety of biological roles from adipogenesis to carcinogenesis. More ligands (agonist and antagonist) are needed to explore the multiple functions of PPAR, particularly PPARgamma. In order to complete such ligand screening, a binding test should be assessed versus the classical transactivation reporter gene assay. In the present work, the full-length human PPARgamma protein as well as its ligand binding domain portion were expressed in Escherichia coli. Bacterial membrane preparations expressing those constructs were characterized using a classical binding competition assay [3H]rosiglitazone as the radioligand. When the receptor preparations were soluble, binding had to be measured with a new alternative method. The systems were assessed using a series of reference PPAR (alpha, beta and gamma) ligands. The full-length human PPARgamma fused to glutathione-S-transferase, expressed in E. coli and tested as a bacterial membrane-bound protein led to the most accurate results when compared to the literature. Furthermore, in an attempt to complete the panel of natural PPARgamma ligands, 29 commercially available prostaglandins were screened in the binding assay. Prostaglandins H(1) and H(2) were found to be modest ligands, however as potent as 15Delta(12-14 )prostaglandin J(2). These results were confirmed in the classical transactivation assay. The fact that these three prostaglandins were equally potent, suggests new pathways of PPARgamma-linked gene activation.

Antitumor activity, optimum administration method and pharmacokinetics of 13,14-dihydro-15-deoxy-deoxy-Delta7 -prostaglandin A1 methyl ester (TEI-9826) integrated in lipid microspheres (Lipo TEI-9826)

13,14-Dihydro-15-deoxy-Delta7-prostaglandin A1 methyl ester (TEI-9826), an antitumor prostaglandin analog, is a candidate for clinical trial. In the present study, we examined its biological stability in vitro, antitumor activity in vitro and in vivo, and pharmacokinetics. Although TEI-9826 was rapidly hydrolyzed to the carboxylic acid form (TOK-4528), TOK-4528 as well as Delta12-prostaglandin J2 (PGJ2) were found to be stable in rat, mouse and human serum in vitro. TEI-9826 exhibited nearly identical or greater potential antitumor activity compared to Delta12-PGJ2 and Delta7-PGA1 in vitro against Colon26 tumor cells. Further evaluation of TEI-9826 using the 38 human cancer cell lines panel and COMPARE analysis suggested that its mode of action is quite different from other anticancer agents that are currently used. TEI-9826 was integrated into lipid microspheres (Lipo TEI-9826) for dosing. Growth inhibition by Lipo TEI-9826 against Colon26 tumor inoculated s.c. in mice depended on administration route, i.e. at 80 mg/kg, no growth suppressive effect was observed for daily bolus i.v., but significant growth suppressive effect was observed for daily i.p., daily s.c. every other day s.c. and 4 times a day continuous (5 min) i.v. These tumor growth-suppressive effects were cytostatic and the tumor started to regrow at the end or a few days after the end of administration. The pharmacokinetic study suggested that maintaining the blood level of TEI-9826 and/or TOK-4528 was essential for their antitumor effects. These results show that continuous i.v. infusion might be the most suitable administration method of Lipo TEI-9826 for clinical trial.

A cyclopentenone prostaglandin activates mesangial MAP kinase independently of PPARgamma

The mitogen-activated protein (MAP) kinases mediate the response of renal glomerular mesangial cells to a variety of physiologic and pathologic stimuli. This investigation examines the effect of the cyclopentenone prostaglandin 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2) on MAP kinases in human mesangial cells. We show that 15d-PGJ2 dose-dependently increases the extracellular signal-regulated kinase (ERK) activity of human mesangial cells, but has no effect on Jun-NH2-terminal kinase or p38 MAP kinase. Despite the fact that 15d-PGJ2 is a peroxisome proliferator-activated receptor (PPAR) ligand, and PPARgamma is shown to be expressed by mesangial cells, the thiazolidinedione PPARgamma agonist ciglitazone does not activate ERK. Additionally, a synthetic PPARgamma antagonist does not attenuate the activation of ERK by 15d-PGJ2. 15d-PGJ2-mediated ERK activation is however blocked by the MEK inhibitor PD 098059, appears to require phosphatidylinositol-3 kinase, but is independent of protein kinase C activation. These results demonstrate a novel effect of 15d-PGJ2 to induce ERK in human mesangial cells independently of PPARgamma.

Resistance to melanoma metastases in mice selected for high acute inflammatory response

The role of innate immunity in natural resistance to tumor progression was investigated in two mouse lines, AIRmax and AIRmin, selected by bi-directional selective breeding on the basis of high or low acute inflammatory response. Compared with AIRmin, AIRmax mice were shown to be resistant to 7,12-dimethylbenz[a]anthracene (DMBA)/12-O:-tetradecanoylphorbol-13-acetate-induced skin cancers and here we demonstrate that AIRmax are also able to restrain the development of metastases upon transfer of MHC compatible, incompatible or xenogeneic melanomas. An acute inflammatory response to melanoma cells was observed in AIRmax mice only, although both lines were found to mount similar specific immune responses to melanoma antigens. The genetically selected lines therefore represent a model system to analyze the positive correlation between multiple resistance to tumorigenesis and host inflammatory responsiveness.

Transcriptional regulation of prostaglandin-H-synthase-1 in the amnion-derived AV3 cell line

Prostaglandin-H-synthase-1 (PGHS-1), while constitutively expressed in most tissues, increases in abundance in human gestational membranes at term. This suggests that PGHS-1 may be up-regulated in preparation for labor, and thus might be a key determinant in timing labor onset. We conducted transient transfection experiments in amnion-derived AV3 cells utilizing pPGHS1CAT to identify substances that might regulate PGHS-1 expression in amnion. Transforming growth factor-beta (1 ng/ml) and 15-deoxy-delta(12,14) prostaglandin J2 (1 microM) significantly (P < 0.05) (33% and 44% respectively) increased PGHS-1 promoter activity. The activity decreased significantly (P < 0.05) in response to interleukin-1 (IL-1)beta (1 ng/ml) (45%), tumor necrosis factor (TNF)-alpha (50 ng/ml) (34%), epidermal growth factor (10 ng/ml) (54%), phorbol myristate acetate (10 nM) (70%), IL-4 (10 ng/ml) (50%), IL-8 (100 ng/ml) (72%) and Activin A (25 ng/ml) (32%). Whether this degree of change in promoter activity leads to physiologically relevant alterations in the amounts of PGHS-1 present in cells remains to be determined.

Peroxisome proliferator activator receptor-gamma agonists and 15-deoxy-Delta(12,14)(12,14)-PGJ(2) induce apoptosis in normal and malignant B-lineage cells

The research described herein evaluates the expression and functional significance of peroxisome proliferator activator receptor-gamma (PPAR-gamma) on B-lineage cells. Normal mouse B cells and a variety of B lymphoma cells reflective of stages of B cell differentiation (e.g., 70Z/3, CH31, WEHI-231, CH12, and J558) express PPAR-gamma mRNA and, by Western blot analysis, the 67-kDa PPAR-gamma protein. 15-Deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)), a PPAR-gamma agonist, has a dose-dependent antiproliferative and cytotoxic effect on normal and malignant B cells as shown by [(3)H]thymidine and 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide assays. Only PPAR-gamma agonists (thiazolidinediones), and not PPAR-alpha agonists, mimicked the effect of 15d-PGJ(2) on B-lineage cells, indicating that the mechanism by which 15d-PGJ(2) negatively affects B-lineage cells involves in part PPAR-gamma. The mechanism by which PPAR-gamma agonists induce cytotoxicity is via apoptosis, as shown by annexin V staining and as confirmed by DNA fragmentation detected using the TUNEL assay. Interestingly, addition of PGF(2alpha), which was not known to affect lymphocytes, dramatically attenuated the deleterious effects of PPAR-gamma agonists on B lymphomas. Surprisingly, 15d-PGJ(2) induced a massive increase in nuclear mitogen-activated protein kinase activation, and pretreatment with PGF(2alpha) blunted the mitogen-activated protein kinase activation. This is the first study evaluating PPAR-gamma expression and its significance on B lymphocytes. PPAR-gamma agonists may serve as a counterbalance to the stimulating effects of other PGs, namely PGE(2), which promotes B cell differentiation. Finally, the use of PGs, such as 15d-PGJ(2), and synthetic PPAR-gamma agonists to induce apoptosis in B-lineage cells may lead to the development of novel therapies for fatal B lymphomas.

Preparation and evaluation of o/w type emulsions containing antitumor prostaglandin

Antitumor prostaglandins(PGs) such as Delta12-PGJ2 and Delta7-PGA1 possess a cyclopentenone or cross-conjugated dienone structures. Antitumor PGs are actively incorporated through cell membrane and control gene expression. Very recent studies clarified that P53 independent expression of p21 and gadd 45, activation of PPARgamma are involved in antitumor mechanism of these PGs. At the low concentration, these PGs exhibit physiological or pathological activity such as osteoblast calcification, promotion of colon cancer cell proliferation. COMPARE PROGRAM using human 38 tumor cell lines suggested that antitumor mechanism of Delta7-PGA1 and 13, 14-dihydro-15-deoxy-Delta7-PGA1 methyl ester (TEI-9826) are quite different from other anticancer agents which are clinically used. Lipid microspheres and Lipiodol formulation were examined as dosage form of the PGs and lipid microspheres were selected for further study. At first lipid microspheres integrated TEI-9038 (Lipo TEI-9038) was chosen as a candidate for clinical trial. However Lipo TEI-9038 failed to exhibit substantial antitumor effect because of its enzymatic instability and toxicity in vivo. Lipo TEI-9826 was then selected as promising candidate for clinical trial because of its stability in serum. Lipo TEI-9826 exhibited marked antitumor effect in several animal models including CDDP resistant nude mice model. Pharmacokinetic and toxicological studies using rats suggested that continuous infusion is the most suitable administration method for Lipo TEI-9826. New type emulsifier, Controlled High Pressure Process Homogenizer (De-BEE 2000 and mini De-BEE) was developed during the preclinical studies on manufacturing process of Lipo TEI-9826. These results warrant the clinical trial for Lipo TEI-9826 in CDDP resistant cancer.

15-Deoxy-Delta(12,14)-prostaglandin J(2) facilitates thyroglobulin production by cultured human thyrocytes

A cyclopentenone-type prostaglandin, 15-deoxy-Delta(12, 14)-prostaglandin J(2) (15-d-PGJ(2)), has been shown to induce the cellular stress response and to be a ligand for the peroxisome proliferator-activated receptor (PPAR)-gamma. We studied its effect on the basal and thyrotropin (TSH)-induced production of thyroglobulin (TG) by human thyrocytes cultured in the presence of 10% FBS. In 15-d-PGJ(2)-treated cells in which the agent itself did not stimulate cAMP production, both the basal production of TG and the response to TSH were facilitated, including the production of TG and cAMP, whereas such production was decreased in untreated cells according to duration of culture. PGD(2) and PGJ(2), which are precursors to 15-d-PGJ(2), exhibited an effect similar to 15-d-PGJ(2). However, the antidiabetic thiazolidinediones known to be specific ligands for PPAR-gamma, and WY-14643, a specific PPAR-alpha ligand, lacked this effect. 15-d-PGJ(2) and its precursors, but not the thiazolidinediones, induced gene expression for heme oxygenase-1 (HO-1), a stress-related protein, and strongly inhibited interleukin-1 (IL-1)-induced nitric oxide (NO) production. Cyclopentenone-type PGs have been recently shown to inhibit nuclear factor-kappaB (NF-kappaB) activation via a direct and PPAR-independent inhibition of inhibitor-kappaB kinase, suggesting that, in human thyrocytes, such PGs may inhibit IL-1-induced NO production, possibly via an inhibition of NF-kappaB activation. On the other hand, sodium arsenite, a known activator of the stress response pathway, induced HO-1 mRNA expression but lacked a promoting effect on TG production. Thus 15-d-PGJ(2) and its precursors appear to facilitate TG production via a PPAR-independent mechanism and through a different pathway from the cellular stress response that is available to cyclopentenone-type PGs. Our findings reveal a novel role of these PGs associated with thyrocyte differentiation.

Biochemical, structural, genetic, physiological, and pathophysiological features of lipocalin-type prostaglandin D synthase

Lipocalin-type prostaglandin (PG) D synthase (PGDS) catalyzes the isomerization of PGH(2), a common precursor of various prostanoids, to produce PGD(2), a potent endogenous somnogen and nociceptive modulator, in the presence of sulfhydryl compounds. PGDS is an N-glycosylated monomeric protein with an M(r) of 20000-31000 depending on the size of the glycosyl moiety. PGDS is localized in the central nervous system and male genital organs of various mammals and in the human heart and is secreted into the cerebrospinal fluid, seminal plasma, and plasma, respectively, as beta-trace. The PGDS concentrations in these body fluids are useful for the diagnosis of several neurological disorders, dysfunction of sperm formation, and cardiovascular and renal diseases. The cDNA and gene for PGDS have been isolated from several animal species, and the tissue distribution and cellular localization have also been determined. This enzyme is considered to be a dual functional protein; i.e. it acts as a PGD(2)-producing enzyme and also as a lipophilic ligand-binding protein, because the enzyme binds biliverdin, bilirubin (K(d)=30 nM), retinaldehyde, retinoic acid (K(d)=80 nM) with high affinities. X-ray crystallographic analyses revealed that PGDS possesses a beta-barrel structure with a hydrophobic pocket in which an active thiol, Cys(65), the active center for the catalytic reaction, was located facing to the inside of the pocket. Gene-knockout and transgenic mice for PGDS were generated and found to have abnormalities in the regulation of nociception and sleep.

Designed cyclopentenone prostaglandin derivatives as neurite outgrowth-promoting compounds for CAD cells, a rat catecholaminergic neuronal cell line of the central nervous system

Here we reported the effects of neurite outgrowth-promoting prostaglandins (NEPP's) on neurons of the central nervous system (CNS). Serum deprivation promoted neurite outgrowth from CAD cells, a CNS-derived cathecholaminergic neuronal cell line. NEPP's (0.05-0.2 microM) accelerated the neurite outgrowth from CAD cells in serum-free medium but didn't in serum-containing medium. Through the study of structure-function relationship with the NEPP's 1-10, NEPP 10 (13,14-dihydro-15-epi-Delta(7)-prostaglandin A(1) (methyl ester) revealed the best compound, exhibiting potent neurite outgrowth-promoting activity with minimal cytotoxicity, suggesting that it is the best compound for drug development.

Feedback control of cyclooxygenase-2 expression through PPARgamma

Cyclooxygenase-2 (COX-2), a rate-limiting enzyme for prostaglandins (PG), plays a key role in inflammation, tumorigenesis, development, and circulatory homeostasis. The PGD(2) metabolite 15-deoxy-Delta(12, 14) PGJ(2) (15d-PGJ(2)) was identified as a potent natural ligand for the peroxisome proliferator-activated receptor-gamma (PPARgamma). PPARgamma expressed in macrophages has been postulated as a negative regulator of inflammation and a positive regulator of differentiation into foam cell associated with atherogenesis. Here, we show that 15d-PGJ(2) suppresses the lipopolysaccharide (LPS)-induced expression of COX-2 in the macrophage-like differentiated U937 cells but not in vascular endothelial cells. PPARgamma mRNA abundantly expressed in the U937 cells, not in the endothelial cells, is down-regulated by LPS. In contrast, LPS up-regulates mRNA for the glucocorticoid receptor which ligand anti-inflammatory steroid dexamethasone (DEX) strongly suppresses the LPS-induced expression of COX-2, although both 15d-PGJ(2) and DEX suppressed COX-2 promoter activity by interfering with the NF-kappaB signaling pathway. Transfection of a PPARgamma expression vector into the endothelial cells acquires this suppressive regulation of COX-2 gene by 15d-PGJ(2) but not by DEX. A selective COX-2 inhibitor, NS-398, inhibits production of PGD(2) in the U937 cells. Taking these findings together, we propose that expression of COX-2 is regulated by a negative feedback loop mediated through PPARgamma, which makes possible a dynamic production of PG, especially in macrophages, and may be attributed to various expression patterns and physiological functions of COX-2.

Facilitatory roles of novel compounds designed from cyclopentenone prostaglandins on neurite outgrowth-promoting activities of nerve growth factor

Cyclopentenone prostaglandins (PGs) are known to arrest the cell cycle at the G(1) phase in vitro and to suppress tumor growth in vivo. However, their effects on neurons are unclear. Here, we report that some cyclopentenone PGs function as neurite outgrowth-promoting factors. They promoted neurite outgrowth from PC12 cells and from dorsal root ganglion explants but only in the presence of nerve growth factor (NGF). We refer to these PGs as neurite outgrowth-promoting PGs (NEPPs). Through study of the structure-function relationship of NEPP1-10 and related compounds, we found that the cross-conjugated dienone moiety of NEPPs was essential for promoting neurite outgrowth, and NEPP10 was concluded to be the best candidate for drug development. We also investigated the intracellular mechanism of the promotion by NEPPs and obtained evidence that immunoglobulin heavy chain binding protein/glucose-regulated protein 78 (BiP/GRP78) plays a role in the promotion, based on the following observations: Antisense nucleotides for BiP/GRP78 gene blocked the promotion of neurite outgrowth; BiP/GRP78 protein level increased in response to NEPPs; and overexpression of BiP/GRP78 protein by adenoviral gene transfer promoted the neurite outgrowth by NGF.