15-deoxy-delta(12,14)-PGJ(2) induces synoviocyte apoptosis and suppresses adjuvant-induced arthritis in rats

Anti-inflammatory effects of PPAR-gamma agonists directly correlate with PPAR-gamma expression during acute pancreatitis

Peroxisome proliferator-activated receptors (PPARs) are ligand-inducible transcription factors that regulate cellular energy and lipid metabolism. PPAR-gamma agonists also have potent anti-inflammatory properties through down-regulation of early inflammatory response genes. The role of PPAR-gamma in acute pancreatitis has not been adequately examined. In this study, we determined the effect of PPAR-gamma agonists on the severity of pancreatitis and sought to correlate PPAR-gamma expression in pancreatic acinar cells and the severity of acute pancreatitis in vivo. Acute pancreatitis was induced in mice by hyperstimulation with the cholecystokinin analog, cerulein. PPAR-gamma agonists were administered by intraperitoneal injection 15-30 minutes before induction of pancreatitis (pretreatment) or at various times after induction of pancreatitis (treatment). Pancreata and serum were harvested over the course of 24 hours. Serum amylase activity and glucose levels were measured. Pancreata were used for histological evaluation as well as protein and mRNA analysis. Pretreatment of mice with the PPAR-gamma agonists 15-deoxy-Delta12, 14-prostaglandin J(2), or troglitazone significantly reduced the severity of pancreatitis in a dose-dependent manner. This reduction was indicated by reduced serum amylase activity and histological damage (leukocyte infiltration, vacuolization, and necrosis). Although cerulein decreased PPAR-gamma expression in the pancreas, pretreatment with agonists maintained PPAR-gamma expression early in acute pancreatitis. The expression of PPAR-gamma inversely correlated with pancreatitis severity and expression of the proinflammatory cytokines, interleukin-6, and tumor necrosis factor-alpha. Treatment with troglitazone after the induction of pancreatitis reduced serum amylase activity. The results suggest that PPAR-gamma plays a direct role in the inflammatory cascade during the early events of acute pancreatitis. Our data are the first to demonstrate that PPAR-gamma agonists represent a promising therapeutic strategy for acute pancreatitis.

PPARgamma antagonists reverse the inhibition of neural antigen-specific Th1 response and experimental allergic encephalomyelitis by Ciglitazone and 15-deoxy-Delta12,14-prostaglandin J2

Peroxisome proliferator-activated receptor-gamma is a nuclear receptor transcription factor that regulates cell growth, differentiation and homeostasis. PPARgamma agonists have been used to treat obesity, diabetes, cancer and inflammation and recent studies have shown the protective effects of PPARgamma agonists on experimental allergic encephalomyelitis (EAE), a Th1 cell-mediated autoimmune disease model of multiple sclerosis (MS). Our studies have further demonstrated that the PPARgamma agonists, 15d-PGJ2 and Ciglitazone, inhibit EAE through blocking IL-12 signaling leading to Th1 differentiation and the PPARgamma deficient heterozygous mice (PPARgamma+/-) or those treated with PPARgamma antagonists develop an exacerbated EAE in association with an augmented Th1 response. In this study, we show that the PPARgamma antagonists, Bisphenol A diglycidyl ether (BADGE) and 2-chloro-5-nitro-N-(4-pyridyl)benzamide (T0070907), reverse the inhibition of EAE by the PPARgamma agonists, Ciglitazone and 15-Deoxy-Delta(12,14)-Prostaglandin J2, in C57BL/6 wild-type and PPARgamma+/- mice. The reversal of EAE by BADGE and T0070907 was associated with restoration of neural antigen-induced T cell proliferation, IFNgamma production and Th1 differentiation inhibited by Ciglitazone and 15d-PGJ2. These results suggest that Ciglitazone and 15d-PGJ2 ameliorate EAE through PPARgamma-dependent mechanisms and further confirm a physiological role for PPARgamma in the regulation of CNS inflammation and demyelination in EAE.

Peroxisome proliferator-activated receptor-alpha and retinoid X receptor agonists inhibit inflammatory responses of astrocytes

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) plays a key role in lipid metabolism and inflammation. Recently, we demonstrated that administration of the PPAR-alpha agonists gemfibrozil and fenofibrate, inhibit the clinical signs of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). In the present study, we investigated the effects of PPAR-alpha agonists on primary mouse astrocytes, a cell type implicated in the pathology of MS and EAE. Our studies demonstrated that the PPAR-alpha agonists fenofibrate, and WY 14643 inhibited NO production by LPS-stimulated astrocytes in a dose-dependent manner. Additionally, PPAR-alpha agonists inhibited the secretion of the pro-inflammatory cytokines TNF-alpha, IL-1beta, and IL-6 by LPS-stimulated astrocytes. Fenofibrate inhibited NF-kappaB DNA binding activity, suggesting a mechanism by which PPAR-alpha agonists may regulate the expression of genes encoding these pro-inflammatory molecules. Retinoid X receptors (RXRs) physically interact with PPAR-alpha receptors, and the resulting heterodimers regulate the expression of PPAR-responsive genes. Interestingly, a combination of 9-cis RA and the PPAR-alpha agonists fenofibrate or gemfibrozil cooperatively inhibited NO, TNF-alpha, IL-1beta, IL-6, and MCP-1 production by these cells. Collectively, these results raise the possibility that PPAR-alpha and RXR agonists might be effective in the treatment of MS, where activated astrocytes are believed to contribute to disease pathology.

Prostaglandin E2 synthesis and secretion: The role of PGE2 synthases

Prostaglandin E2 (PGE2) is a principal mediator of inflammation in diseases such as rheumatoid arthritis and osteoarthritis. Nonsteroidal anti-inflammatory medications (NSAIDs) and selective cyclooxygenase-2 (COX-2) inhibitors reduce PGE2 production to diminish the inflammation seen in these diseases, but have toxicities that may include both gastrointestinal bleeding and prothrombotic tendencies. In cells, arachidonic acid is transformed into PGE2 via cyclooxygenase (COX) enzymes and terminal prostaglandin E synthases (PGES). Accumulating data suggest that the interaction of various enzymes in the PGE2 synthetic pathway is complex and tightly regulated. In this review, we summarize the synthesis and secretion of PGE2. In particular, we focus on the three isoforms of the terminal PGES, and discuss the potential of targeting PGES as a more precise strategy for inhibiting PGE2 production.

Folate-targeted immunotherapy effectively treats established adjuvant and collagen-induced arthritis

Activated macrophages express a cell surface receptor for the vitamin folic acid. Because this receptor is inaccessible or not measurably expressed on other normal cells, folic acid has been recently exploited to selectively deliver attached radio-emitters to sites of activated macrophage accumulation, allowing scintigraphic imaging of inflamed joints and organs of arthritic rats. We demonstrate here that folate-linked haptens can also be targeted to activated macrophages, decorating their cell surfaces with highly immunogenic molecules. Under conditions in which the rodent has already been immunized against keyhole limpet hemocyanine-(fluorescein isothiocyanate) FITC, activated macrophages are eliminated. Administration of folate-FITC conjugates to rodents with experimental arthritis attenuates (a) systemic and peri-articular inflammation, (b) bone and cartilage degradation, and (c) arthritis-related body weight loss. Treatment with folate-hapten conjugates is comparable to methotrexate, etanercept, anakinra, and celecoxib at alleviating the symptoms of arthritis. We conclude that reduction of activated macrophages by folate-targeted immunotherapy can ameliorate the symptoms of arthritis in two rodent models of the disease.

Sphingosine 1-phosphate/sphingosine 1-phosphate receptor 1 signaling in rheumatoid synovium: regulation of synovial proliferation and inflammatory gene expression

OBJECTIVE

Sphingosine 1-phosphate (S1P) is involved in various pathologic conditions and has been implicated as an important mediator of angiogenesis, inflammation, cancer, and autoimmunity. This study was undertaken to examine the role of S1P/S1P1 signaling in the pathogenesis of rheumatoid arthritis (RA).

METHODS

We examined S1P1 messenger RNA (mRNA) and protein levels in RA synoviocytes and MH7A cells by reverse transcriptase-polymerase chain reaction and Western blotting. We also performed S1P1 immunohistochemistry analysis in synovial tissue from 28 RA patients and 18 osteoarthritis (OA) patients. We investigated the effects of S1P on proliferation by WST-1 assay, and its effects on tumor necrosis factor alpha (TNFalpha)- or interleukin-1beta (IL-1beta)-induced cyclooxygenase 2 (COX-2) expression and prostaglandin E2 (PGE2) production in RA synoviocytes and MH7A cells by Western blotting and enzyme-linked immunosorbent assay, respectively. Finally, we examined whether these effects of S1P were sensitive to pertussis toxin (PTX), an inhibitor of the Gi/Go proteins.

RESULTS

S1P1 mRNA and protein were detected in RA synoviocytes and MH7A cells. S1P1 was more strongly expressed in synovial lining cells, vascular endothelial cells, and inflammatory mononuclear cells of RA synovium compared with OA synovium. S1P increased the proliferation of RA synoviocytes and MH7A cells. S1P alone significantly enhanced COX-2 expression and PGE2 production. Moreover, S1P enhanced expression of COX-2 and production of PGE2 induced by stimulation with TNFalpha or IL-1beta in RA synoviocytes and MH7A cells. These effects of S1P were inhibited by pretreatment with PTX.

CONCLUSION

These findings suggest that S1P signaling via S1P receptors plays an important role in cell proliferation and inflammatory cytokine-induced COX-2 expression and PGE2 production by RA synoviocytes. Thus, regulation of S1P/S1P1 signaling may represent a novel therapeutic target in RA.

Apoptosis of rheumatoid synovial cells by statins through the blocking of protein geranylgeranylation: a potential therapeutic approach to rheumatoid arthritis

OBJECTIVE

To determine whether statins induce apoptosis in rheumatoid arthritis (RA) synoviocytes.

METHODS

The effects of lipophilic and hydrophilic statins (fluvastatin and pravastatin, respectively) on the apoptosis of cultured RA synoviocytes were examined in vitro. Apoptosis was analyzed by flow cytometry after staining with JC-1 (to measure the mitochondrial transmembrane potential), active caspase 3, annexin V, and propidium iodide. Add-back experiments were conducted to determine which downstream products of the mevalonate pathway could suppress apoptosis. Modulation of various signaling pathways induced by statins, including protein prenylation, was also investigated.

RESULTS

Fluvastatin, but not pravastatin, induced apoptosis in RA synoviocytes in a concentration-dependent (1-10 microM) and time-dependent (48-96 hours) manner. Another lipophilic statin, pitavastatin, displayed almost the same effects as fluvastatin. In sharp contrast, lipophilic statins did not significantly increase apoptosis in synoviocytes from patients with osteoarthropathy. Apoptosis induced by fluvastatin was mitochondrial- and caspase 3-dependent and was abrogated by mevalonate and geranylgeranyl pyrophosphate, but not by farnesyl pyrophosphate. In addition, the geranylgeranyl transferase inhibitor GGTI-298 mimicked the effect of fluvastatin on RA synoviocytes. Treatment of RA synoviocytes with the RhoA kinase inhibitor Y-27632 caused apoptosis. Fluvastatin decreased the amount of RhoA protein in the membrane fraction, but increased the amount in the cytosolic fraction.

CONCLUSION

Fluvastatin induced apoptosis in RA synoviocytes through a mitochondrial- and caspase 3-dependent pathway and by the blockage of mevalonate pathways, particularly through the inhibition of protein geranylgeranylation and RhoA/RhoA kinase pathways. These findings suggest that lipophilic statins have potential as novel therapeutic agents for RA.

Neuroprotection against focal ischemic brain injury by the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone

Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is a nuclear membrane-associated transcription factor that governs the expression of various inflammatory genes. PPAR-gamma agonists protect peripheral organs from ischemic injury. In the present study, we investigated whether the PPAR-gamma agonist rosiglitazone is neuroprotective against focal ischemic brain injury. C57/B6 mice underwent 1.5-h middle cerebral artery occlusion, and received either vehicle or rosiglitazone treatment of 0.75, 1.5, 3, 6 or 12 mg/kg (n = 9 per group). Cerebral infarct volume, neurological function, expression of pro-inflammatory proteins and neutrophil accumulation were assessed after ischemia and reperfusion. At 48 h after ischemia, infarct volume was significantly decreased with 3-12 mg/kg of rosiglitazone, with a time window of efficacy of 2 h after ischemia at the optimal dose (6 mg/kg). Neutrophil accumulation was significantly decreased in the brain parenchyma of rosiglitazone-treated mice. Ischemia-induced expression of several inflammatory cytokines and chemokines was markedly reduced in rosiglitazone-treated brains, as determined using proteomic-array analysis. Rosiglitazone treatment improved neurological function at 7 days after ischemia. Moreover, in cultured cortical primary microglia, rosiglitazone attenuated inflammatory responses by decreasing lipopolysaccharide-induced release of tumor necrosis factor-alpha, interleukin (IL)-1beta and IL-6. These results suggest that the PPAR-gamma agonist rosiglitazone has neuroprotective properties that are at least partially mediated via anti-inflammatory actions, and is thus a potential novel therapeutic agent for stroke.

Nuclear receptors and autoimmune disease: the potential of PPAR agonists to treat multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is a T-cell-mediated, autoimmune disorder characterized by central nervous system inflammation and demyelination, features reminiscent of the human disease, multiple sclerosis (MS). Prior work in the EAE model has suggested that encephalitogenic T cells are of the T helper (Th)-1 phenotype. Our group has performed several studies in the EAE model that suggest that a strategy for treating autoimmune disorders is to convert the pathogenic cells from the Th1 to Th2 phenotype. Peroxisome proliferator-activated receptors (PPARs) are members of a nuclear hormone receptor superfamily that include receptors for steroids, retinoids, and thyroid hormone, all of which are known to affect the immune response. Recently, we examined the role of PPARgamma in EAE and observed that administration of the PPARgamma agonist 15-deoxy-Delta(12,14) prostaglandin J2 exerted a significant therapeutic effect predominantly by inhibiting the activation and expansion of encephalitogenic T cells. One potential advantage in studying PPARalpha agonists is that they have been very well tolerated when used in humans to treat conditions such as elevated triglycerides. Building on prior work in immune deviation and with PPAR agonists, we have demonstrated that PPARalpha agonists can alter the cytokine phenotype of myelin-reactive T cells, alter their encephalitogenicity, and be useful in the treatment of EAE. The fact that PPARalpha agonists have been used as therapeutic agents in humans to treat metabolic conditions for over 25 years with little toxicity makes them attractive candidates for use as adjunctive therapies in MS.

Nutrients, nuclear receptors, inflammation, immunity lipids, PPAR, and allergic asthma

The peroxisome proliferator-activated receptors (PPARs) belong to the larger superfamily of steroid/thyroid nuclear receptors. PPARgamma is expressed in a number of hematopoietic cells, including dendritic cells, eosinophils, macrophages, and T cells. A number of lipids and synthetic compounds interact with PPARgamma, that, depending on the cell type, results in the regulation of specific genes. There is now a large body of data indicating that allergic asthma is the result of a predominant type-2 helper T cell immune response including IL-4, -5 and -13, eosinophilic inflammation in the lungs, mucous production, and airway hyperresponsiveness (AHR). Targeting the production of these type-2 helper T cell mediated cytokines has been proposed as a way to regulate this disease. Because PPARgamma ligands can affect T cell cytokine production in vitro, we have examined whether these ligands affect symptoms of allergic asthma in a murine model of this disease. We discuss data showing that ciglitazone and GW1929, two agonistic ligands for PPARgamma, significantly inhibited airway inflammation during allergic asthma induction. Oral treatment with ciglitazone and GW1929 inhibited airway inflammation, with less of an effect on AHR. By contrast, intranasal exposure to GW1929 significantly reduced AHR following exposure to allergen, while GW9662, a PPARgamma antagonist, had no effect. In vitro, T cells from ciglitazone-treated mice secreted significantly less IL-4 and IFN-gamma in response to restimulation. These data suggest that PPARgamma agonists may be useful for the treatment of allergic asthma.

Ganglioside GM3 promotes cell migration by regulating MAPK and c-Fos/AP-1

Gangliosides have been proposed as modulators of transmembrane signaling. Recently, GM3, a glycosphingolipid containing monosaialic acids, is thought to be one of the key molecules of signal transduction in mammalian cells. In this study, we used mouse embryonic fibroblast cell lines (MEFs) established from sialyltransferase-I knockout mice (GM3 synthase KO mice) to evaluate the regulation of mitogenic signals by gangliosides. Cell proliferation assay revealed a higher growth potential of GM3 KO MEFs. Immunoblots showed upregulation of Ras/Raf/MEK/ERK pathway in GM3 KO MEFs, and these signals resulted in enhanced translocation of ERK into the nuclei. Further, both exogenous and endogenous add-back of GM3 decreased the activities of MAPK in GM3 KO MEFs. In addition, GM3 KO MEFs formed foci in high-density culture condition, and analyses of cell cycle modulators revealed the resistance of GM3 KO MEFs for entering cell cycle arrest. Finally, sustained expressions of c-Fos in GM3 KO MEFs were shown to correlate with DNA-binding activity between c-Fos and AP-1. These results demonstrate that the deletion of sialyltransferase-I changes the character of MEFs to a highly activated state of the MAPK pathway, indicating the critical role of GM3 as a regulator of membrane-transmitted signals.

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.

Inflammatory modulation of PPAR gamma expression and activity

Nitric oxide (NO) production increases with age in the lupus-prone MRL/lpr mouse, paralleling disease activity. One mechanism for excess NO production in MRL/lpr mice may be a defect in down-regulatory mechanisms of the iNOS pathway. A potential modulator of NO is the nuclear hormone receptor peroxisome proliferation activated receptor gamma (PPARgamma). We demonstrate that renal PPARgamma protein expression was altered as disease progressed in MRL/lpr mice, which paralleled increased iNOS protein expression. Additionally, MRL/lpr-derived primary mesangial cells expressed less PPARgamma than BALB/c mesangial cells and produced more NO in response to LPS and IFNgamma. Furthermore, PPARgamma activity was reduced in mesangial cells following exposure to inflammatory mediators. This activity was restored with the addition of a NOS enzyme inhibitor. These results indicate that the activation of inflammatory pathways may lead to reduced activity and expression of PPARgamma, further exacerbating the disease state.

Agonists for the peroxisome proliferator-activated receptor-alpha and the retinoid X receptor inhibit inflammatory responses of microglia

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) plays a key role in lipid metabolism and inflammation. Recently, we demonstrated that administration of the PPAR-alpha agonists gemfibrozil and fenofibrate, inhibit the clinical signs of experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). In the present study we investigated the effects of PPAR-alpha agonists on primary mouse microglia, a cell type implicated in the pathology of MS and EAE. Our studies demonstrated that the PPAR-alpha agonists ciprofibrate, fenofibrate, gemfibrozil, and WY 14,643 each inhibited NO production by cytokine-stimulated microglia in a dose-dependent manner. However, fenofibrate and WY 14,643 were more potent inhibitors than gemfibrozil and ciprofibrate. In LPS-stimulated microglia, only fenofibrate and WY 14,643 significantly suppressed NO production. Additionally, PPAR-alpha agonists inhibited the secretion of the proinflammatory cytokines IL-1beta, TNF-alpha, IL-6, and IL-12 p40 and the chemokine MCP-1 by LPS-stimulated microglia. Retinoid X receptors (RXRs) physically interact with PPAR-alpha receptors, and the resulting heterodimers regulate the expression of PPAR-responsive genes. Interestingly, the RXR agonist 9-cis retinoic acid (9-cis RA) inhibited NO production by LPS-stimulated microglia. Furthermore, a combination of 9-cis RA and the PPAR-alpha agonist fenofibrate cooperatively inhibited NO production by these cells. A combination of these agonists also selectively inhibited the expression of proinflammatory cytokines including IL-1beta, TNF-alpha, and IL-6 by LPS-stimulated microglia. Collectively, these results raise the possibility that PPAR-alpha and RXR agonists might have benefit as a therapy in MS, where activated microglia are believed to contribute to disease pathology.

Peroxisome proliferator-activated receptor-gamma is a new therapeutic target in sepsis and inflammation

Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a member of the nuclear receptor superfamily and a ligand-activated transcription factor with pleiotropic effects on lipid metabolism, inflammation, and cell proliferation. PPARgamma forms a heterodimer with the retinoid X receptor and upon ligand-activation binds to the PPAR response element in the promoter of genes to allow transcription. The class of insulin-sensitizing drugs known as thiazolidinediones have been identified as specific PPARgamma agonists that have allowed the characterization of many genes regulated by PPARgamma. Thiazolidinediones include rosiglitazone, pioglitazone, troglitazone, and ciglitazone. In addition to these synthetic agonists, cyclopentenone prostaglandins of the J2 series have been identified as natural ligands for PPARgamma. Several in vitro and in vivo studies have demonstrated that pharmacological activation of PPARgamma by 15-deoxy-Delta(12,14)-PGJ2 (15d-PGJ2) or thiazolidinediones has anti-inflammatory effects. This article provides an overview of the role of PPARgamma in regulating the inflammatory response and emphasizes the potential efficacy of PPARgamma ligands as novel therapeutic approaches beyond diabetes in sepsis, inflammation, and reperfusion injury.

Inhibition of skin sclerosis by 15deoxy delta12,14-prostaglandin J2 and retrovirally transfected prostaglandin D synthase in a mouse model of bleomycin-induced scleroderma

Hematopoietic prostaglandin D synthase (PGDS) is a key enzyme involved in production of the PGD and J series, which have various role in inflammation and immunity. We evaluated the effect of treatment with 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) or the injection of prostaglandin D(2) synthase (PGDS) cDNA expressing-retrovirally transfected fibroblasts on bleomycin (BLM)-induced scleroderma-like skin sclerosis. Daily injection of BLM (30 microg) for 4 weeks induced histological evidence of dermal sclerosis in C3H mice. We examined the effect of injection of 15d-PGJ(2) (30 ng twice a day) or PGDS expressing-retrovirally transfected fibroblast on BLM-induced dermal sclerosis. Administration of 15d-PGJ(2) (a nonenzymatic metabolite of PGD(2)) injection of PGDS cDNA-expressing fibroblasts significantly reduced dermal sclerosis, the hydroxyproline content, and dermal thickness. Moreover, 15-d PGJ2 down-regulation of the expression of transforming growth factor beta(1) and connective tissue growth factor which had been induced by BLM. Mast cells were also increased in the skin by BLM injection and there was prominent degranulation of these mast cells along with elevated plasma histamine levels. 15-d PGJ(2) and PGDS-expressing cells also suppressed degranulation of cultured mast cells and histamine release by these cells. These results show that 15-d PGJ(2) and PGDS-expressing cells can prevent experimental skin sclerosis induced by BLM and raise the possibility of therapeutic approaches targeting of PPARgamma for the skin lesion of scleroderma.

Effect of peroxisome proliferator-activated receptor-gamma ligand on inflammation of human gallbladder epithelial cells

AIM: To investigate the effect of peroxisome proliferator-activated receptor gamma (PPAR-γ) and its ligand, ciglitazone, on inflammatory regulation of human gallbladder epithelial cells (HGBECs) and to assess the effect of human epithelial growth factor (hEGF) on growth of HGBECs.

METHODS: HGBECs were cultured in media containing hEGF or in hEGF-free media. HGBECs were divided into normal control group, inflammatory control group and ciglitazone group (test group). Inflammatory control group and ciglitazone group were treated with 5 mg/L of human interleukin-1β (hIL-1β) to make inflammatory model of HGBECs. The ciglitazone group was treated with various concentrations of ciglitazone, a potent ligand of PPAR-γ. Subsequently, interleukin-8 (IL-8), IL-6, and tumor necrosis factor-a (TNF-α) concentrations in all groups were measured. The data were analyzed statistically.

RESULTS: HGBECs were cultured in medium successfully. The longevity of HGBECs in groups containing hEGF was longer than that in hEGF-free groups. So was the number of HGBECs. The longest survival time of HGBEC was 25 d. The inflammatory model of HGBECs was obtained by treating with hIL-1β. The concentrations of IL-6 and IL-8 in ciglitazone group were lower than those in inflammatory control group (P<0.05). The secretion of IL-6 in inflammatory control group was higher (350.3137.05 mg/L) than that in normal control group (50.00.00 mg/L, P<0.001). Compared to normal control group, IL-8 concentration in inflammatory control was higher (P<0.05).

CONCLUSION: hEGF improves the growth of HGBECs in vitro. Ciglitazone inhibits the inflammation of HGBECs in vitro and has potential therapeutic effect on cholecystitis in vivo.

Electro-transfer of small interfering RNA ameliorated arthritis in rats

RNA interference provides the powerful means of sequence-specific gene silencing. Particularly, small interfering RNA (siRNA) duplexes may be potentially useful for therapeutic molecular targeting of human diseases, although novel delivery systems should be devised to achieve efficient and organ-specific transduction of siRNA. In the present study, we demonstrated that electro-transfer of a siRNA-polyamine complex made efficient and specific gene knockdown possible in the articular synovium. Targeted suppression of the tumor necrosis factor-alpha gene through this procedure significantly ameliorated collagen-induced arthritis in rats. Our results suggest the potential feasibility of therapeutic intervention with RNA medicines for treatment of rheumatoid and other locomotor diseases.

PPARγ antagonists exacerbate neural antigen-specific Th1 response and experimental allergic encephalomyelitis

Peroxisome proliferator-activated receptor-gamma is a nuclear receptor transcription factor that regulates cell growth, differentiation and homeostasis. PPARgamma agonists have been used in the treatment of obesity, diabetes, cancer and inflammation. We and others have shown recently that PPARgamma agonists ameliorate experimental allergic encephalomyelitis (EAE), a Th1 cell-mediated autoimmune disease model of multiple sclerosis (MS). We have further shown that PPARgamma agonists inhibit EAE through blocking IL-12 signaling leading to Th1 differentiation and the PPARgamma-deficient heterozygous mice (PPARgamma(+/-)) develop an exacerbated EAE. In this study, we show that in vivo treatment (i.p.) with 100 mug PPARgamma antagonists, Bisphenol A diglycidyl ether (BADGE) or 2-Chloro-5-nitro-N-(4-pyridyl)benzamide (T0070907), on every other day from day 0 to 30, increased the severity and duration of EAE in C57BL/6 wild-type and PPARgamma(+/-) mice. The exacerbation of EAE by PPARgamma antagonists associates with an augmented neural antigen-induced T cell proliferation, IFNgamma production or Th1 differentiation. These results further suggest that PPARgamma is a critical physiological regulator of CNS inflammation and demyelination in EAE.

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

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

Ciglitazone inhibits the antigen-induced leukotrienes production independently of PPARgamma in RBL-2H3 mast cells

Peroxisome prolifelator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor, through which PPARgamma agonists have been demonstrated to down-regulate inflammatory cell functions. Recently, the agonists are reported to exert, in some conditions, their inhibitory actions independently of PPARgamma. Previously, we showed that a PPARgamma agonist, troglitazone, inhibited cysteinyl (Cys)-leukotrienes production in RBL-2H3 cells after IgE receptor triggering. Here we examined whether the inhibition of cycteinyl-leukotrienes production in the cells was dependent on the activation of PPARgamma. A PPARgamma agonist, ciglitazone, significantly inhibited Cys-leukotrienes, but not prostaglandin D2, production. The inhibition was not attenuated by the pretreatment with a PPARgamma antagonist. Ciglitazone did not alter the mRNA expression of acyl-coenzyme A binding protein, the gene expression of which is up-regulated by PPARgamma, nor induce the nucleus translocation of PPARgamma. These results suggest that the inhibition by PPARgamma agonists of Cys-leukotrienes production in RBL-2H3 cells after IgE receptor triggering is not through the activation of PPARgamma.

Peroxisome proliferator-activated receptors and inflammation

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptors family. PPARs are a family of 3 ligand-activated transcription factors: PPARalpha (NR1C1), PPARbeta/delta (NUC1; NR1C2), and PPARgamma (NR1C3). PPARalpha, -beta/delta, and -gamma are encoded by different genes but show substantial amino acid similarity, especially within the DNA and ligand binding domains. All PPARs act as heterodimers with the 9-cis-retinoic acid receptors (retinoid X receptor; RXRs) and play important roles in the regulation of metabolic pathways, including those of lipid of biosynthesis and glucose metabolism, as well as in a variety of cell differentiation, proliferation, and apoptosis pathways. Recently, there has been a great deal of interest in the involvement of PPARs in inflammatory processes. PPAR ligands, in particular those of PPARalpha and PPARgamma, inhibit the activation of inflammatory gene expression and can negatively interfere with pro-inflammatory transcription factor signaling pathways in vascular and inflammatory cells. Furthermore, PPAR levels are differentially regulated in a variety of inflammatory disorders in man, where ligands appear to be promising new therapies.

Copper chelation with tetrathiomolybdate suppresses adjuvant-induced arthritis and inflammation-associated cachexia in rats

Tetrathiomolybdate (TM), a drug developed for Wilson's disease, produces an anti-angiogenic and anti-inflammatory effect by reducing systemic copper levels. TM therapy has proved effective in inhibiting the growth of tumors in animal tumor models and in cancer patients. We have hypothesized that TM may be used for the therapy of rheumatoid arthritis and have examined the efficacy of TM on adjuvant-induced arthritis in the rat, which is a model of acute inflammatory arthritis and inflammatory cachexia. TM delayed the onset of and suppressed the severity of clinical arthritis on both paw volume and the arthritis score. Histological examination demonstrated that TM significantly reduces the synovial hyperplasia and inflammatory cell invasion in joint tissues. Interestingly, TM can inhibit the expression of vascular endothelial growth factor in serum synovial tissues, especially in endothelial cells and macrophages. Moreover, the extent of pannus formation, which leads to bone destruction, is correlated with the content of vascular endothelial growth factor in the serum. There was no mortality in TM-treated rat abnormalities. TM also suppressed inflammatory cachexia. We suggest that copper deficiency induced by TM is a potent approach both to inhibit the progression of rheumatoid arthritis with minimal adverse effects and to improve the well-being of rheumatoid arthritis patients.

A novel PPAR response element in the murine iNOS promoter

The nuclear hormone receptor peroxisome proliferation activated receptor gamma (PPARgamma) is a modulator of inflammation including down-regulation of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production. PPARgamma agonists reduce iNOS expression and NO production in a dose-dependent manner in macrophages, mesangial cells and other inflammatory cells. However, the mechanisms involved in the inhibition of iNOS expression by PPARgamma and its agonists are not fully understood. Here we show that the PPARgamma agonist ciglitazone dose-dependently inhibited a murine iNOS-luciferase reporter construct by up to 50% in transfected mesangial cells. Blocking de novo protein synthesis in mesangial cells had no effect on PPARgamma agonist activity, indicating that ciglitazone acts directly to inhibit iNOS transcription. We identified a novel PPAR response element (PPRE) in the murine iNOS promoter that is homologous to the PPRE consensus sequence. In binding assays PPARgamma directly binds to this response element in vitro and can function as a positive element in response to PPARgamma agonists when placed in front of a reporter gene. Site-directed mutagenesis of this PPRE in a murine iNOS promoter/reporter construct did not block the inhibitory activity of a synthetic PPARgamma agonist on the iNOS promoter/reporter construct in transfected mesangial cells. However, the mutated construct exhibited lower basal expression, and higher expression in response to inflammatory stimuli compared to the intact construct. These data suggest that the iNOS PPRE contributes to positive basal expression and negative expression of iNOS in response to inflammatory stimuli. The PPRE is not necessary, however, for synthetic PPARgamma agonists to inhibit iNOS expression.

Nanomolar and micromolar effects of 15-deoxy-delta 12,14-prostaglandin J2 on amnion-derived WISH epithelial cells: differential roles of peroxisome proliferator-activated receptors gamma and delta and nuclear factor kappa B

15-Deoxy delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), an activator of peroxisome proliferator-activated receptor (PPAR)-gamma and -delta, is a prostanoid metabolite with anti-inflammatory actions. In intrauterine tissues, proinflammatory cytokines and prostaglandins have been identified as playing key roles in the maintenance of pregnancy and the onset of labor. We investigated and compared the early (<3 h) effects of 15d-PGJ(2) with rosiglitazone (PPAR-gamma ligand) and 2-methyl-4-((4-methyl-2-(4-trifluoromethylphenyl)-1,3-thiazol-5-yl)-methylsulfanyl)phenoxy-acetic acid (GW501516) (PPAR-delta ligand) on interleukin (IL)-1beta-induced prostaglandin and cytokine production by amnion-derived WISH cells. We show that 15d-PGJ(2) exerts differential effects depending on concentration. At low concentrations (<0.1 microM), 15d-PGJ(2) inhibited IL-1beta-stimulated prostaglandin E(2) (PGE(2)) but not cytokine (IL-6/IL-8) production or cyclooxygenase-2 (COX-2) expression. This effect was attenuated by a PPAR-gamma inhibitor [2-chloro-5-nitro-N-phenyl-benzamide (GW9662)], by transfection with a dominant-negative PPAR construct, and was reproduced by the PPAR-gamma ligand rosiglitazone. At higher concentrations (1-10 microM), 15d-PGJ(2) inhibited IL-1beta-stimulated PGE(2) and cytokine production and COX-2 expression, and this effect was not blocked by GW9662. Rosiglitazone at high concentrations (1-10 microM) stimulated PGE(2) production in the absence or presence of the dominant-negative PPAR. The PPAR-delta ligand GW501516 also inhibited IL-1beta-stimulated PGE(2) production but only at high concentrations (1 microM). IL-1beta-induced nuclear factor-kappaB (NF-kappaB) DNA binding activity was significantly inhibited by 15d-PGJ(2) (10 microM) and GW501516 (1 microM) but increased with 10 microM rosiglitazone. We conclude that 1) at low concentrations, 15d-PGJ(2) acts through a PPAR-gamma signaling pathway; b) at higher concentrations, its actions are mediated most likely through other pathways such as activation of PPAR-delta and/or inhibition of NF-kappaB; and 3) rosiglitazone exerts PPAR-independent effects at high concentrations (>1 microM).

Up-regulation of cyclooxygenase-2 expression by TSG-6 protein in macrophage cell line

TNF-stimulated gene 6 (TSG-6) encodes a 35 kDa inducible secreted glycoprotein important in inflammation and female fertility. Previous studies have shown that TSG-6 has anti-inflammatory activity in models of acute and chronic inflammation. In the present study, we show that treatment of the RAW 264.7 murine macrophage cell line with TSG-6 protein up-regulates the expression of inducible cyclooxygenase-2 (COX-2), a key enzyme in inflammation and immune responses. This action of TSG-6 protein was abolished by heat denaturation, trypsin digestion, or anti-TSG-6 antibodies. TSG-6 treatment also resulted in a rapid increase in COX-2 mRNA levels, suggesting that TSG-6 up-regulates COX-2 gene expression. Up-regulation of COX-2 was accompanied by an increase in the production of prostaglandins, especially PGD2. As the PGD2 metabolite, 15-deoxy-Delta12,14-PGJ2, can act as a negative regulator of inflammation, these TSG-6 actions may explain, at least in part, the anti-inflammatory effect of TSG-6 observed in the intact organism.

The peroxisome proliferator-activated receptor-gamma ligand 15-deoxyDelta12,14 prostaglandin J2 reduces the organ injury in hemorrhagic shock

The cyclopentenone prostaglandin 15-deoxyDelta12,14PGJ2 (15d-PGJ2) exerts potent anti-inflammatory effects in vivo, which are in part caused by the activation of peroxisome proliferator-activated receptor-gamma (PPAR-gamma). Here we investigate the effects of 15d-PGJ2 on the multiple organ injury/dysfunction associated with severe hemorrhage and resuscitation. Male Wistar rats were subjected to hemorrhage (to lower mean arterial blood pressure to 45 mmHg) for 90 min and subsequently resuscitated with shed blood for 4 h. Rats were treated with either 15d-PGJ2 (0.3 mg/kg i.v.) or its vehicle (10% dimethyl sulfoxide) at 30 min before the hemorrhage. In some experiments, the selective PPAR-gamma antagonist GW9662 (1 mg/kg i.v.) or its vehicle (10% dimethyl sulfoxide) was given 45 min before the hemorrhage. Hemorrhage and resuscitation resulted in an increase in serum levels of (a) urea and creatinine and, hence renal dysfunction; alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and, hence, hepatic injury. The potent PPAR-gamma agonist 15d-PGJ2 abolished the renal dysfunction and largely reduced the liver injury caused by hemorrhagic shock. In addition, 15d-PGJ2 also attenuated the lung and intestinal injury (determined by histology) caused by hemorrhage and resuscitation. The specific PPAR-gamma antagonist GW9662 reduced the protective effects afforded by 15d-PGJ2. 15d-PGJ2 did not affect the delayed fall in blood pressure caused by hemorrhage and resuscitation. The mechanisms of the protective effect of this cyclopentenone prostaglandin are, at least in part, PPAR-gamma dependent, as the protection afforded by 15d-PGJ2 was reduced by the PPAR-gamma antagonist GW9662. We propose that 15d-PGJ2 or other ligands for PPAR-gamma may be useful in the therapy of the organ injury associated with hemorrhagic shock.

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

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

Cyclopentenone prostaglandins PGA2 and 15-deoxy-delta12,14 PGJ2 suppress activation of murine microglia and astrocytes: implications for multiple sclerosis

The cyclopentenone prostaglandin (cPG) 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)) has been identified as a potent antiinflammatory agent that is able to inhibit the activation of macrophages and microglia. Additionally, 15d-PGJ(2) is able to ameliorate the clinical manifestations of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). Many biological effects of 15d-PGJ(2) have been attributed to the peroxisome proliferator activated receptor-gamma (PPAR-gamma). PGA(2), like 15d-PGJ(2), is a cPG. The aim of this study is to compare the relative effectiveness of these two cPGs in inhibiting the inflammatory response of mouse microglia and astrocytes, two cell types that upon activation may contribute to the pathology of EAE and MS. Purified primary mouse microglia and astrocytes were treated with either 15d-PGJ(2) or PGA(2) and then stimulated with either lipopolysaccharide (LPS) or a combination of interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha. The results show that 15d-PGJ(2) and PGA(2) both potently inhibited the production of nitrite, as well as proinflammatory cytokines and chemokines, from microglia and astrocytes. Generally, regulation of NO production was more sensitive to 15d-PGJ(2), however, cytokine and chemokine production was more sensitive to PGA(2) treatment. These results demonstrate for the first time that PGA(2) is a potent antiinflammatory mediator.

Rosiglitazone induces interleukin-1 receptor antagonist in interleukin-1beta-stimulated rat synovial fibroblasts via a peroxisome proliferator-activated receptor beta/delta-dependent mechanism

OBJECTIVE

To study the potency of 2 peroxisome proliferator-activated receptor gamma (PPARgamma) agonists, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-deoxy-PGJ(2)) and rosiglitazone, to modulate the expression of interleukin-1 receptor antagonist (IL-1Ra) in rat synovial fibroblasts.

METHODS

Levels of messenger RNA for IL-1Ra and PPAR isotypes (alpha, beta/delta, gamma) were assessed by real-time polymerase chain reaction in rat synovial fibroblasts exposed to 10 ng/ml of IL-1beta. PPAR levels were assessed by Western blotting and secreted IL-1Ra levels by immunoassay. The potency of PPARgamma agonists and the PPARbeta/delta agonist GW-501516 on IL-1Ra levels was tested in the range of 1-10 microM and at 100 pM, respectively. The contribution of PPARgamma to the effects of rosiglitazone on IL-1Ra secretion was examined either by its overexpression or by inhibition using wild-type or dominant-negative constructs and the antagonist GW-9662 (10 microM), respectively. The dominant-negative strategy was also performed to investigate the possible contribution of PPARbeta/delta and NF-kappaB activation.

RESULTS

IL-1beta-induced IL-1Ra production was increased by 10 microM rosiglitazone but was reduced dose-dependently by 15-deoxy-PGJ(2). Both agonists lowered IL-1beta secretion, but rosiglitazone alone reduced the imbalance of IL-1beta/IL-1Ra toward basal levels. Enhancement of IL-1beta-induced IL-1Ra production by rosiglitazone was not affected by PPARgamma overexpression or by its inhibition with dominant-negative PPARgamma or GW-9662. Inhibition of NF-kappaB was also ineffective against rosiglitazone but abolished the stimulating effect of IL-1beta on IL-1Ra. All PPAR isotypes were expressed constitutively in rat synoviocytes, but PPARgamma decreased dramatically upon IL-1beta exposure, whereas PPARbeta/delta remained stable. Dominant-negative PPARbeta/delta abolished the enhancement of IL-1Ra by rosiglitazone, whereas GW-501516 reproduced the effect of rosiglitazone on IL-1Ra secretion.

CONCLUSION

Rosiglitazone stimulates IL-1Ra production by a PPARbeta/delta mechanism in activated rat synovial fibroblasts, further contributing to its potential antiarthritic properties and opening new perspectives for the modulation of inflammatory genes by specific PPAR agonists in articular cells.

Expression of Peroxisome Proliferator-Activated Receptor-γ in Renal Ischemia-Reperfusion Injury

The pathogenesis of ischemia-reperfusion injury is known to involve cytokines and particularly surface adhesion molecules, the expression of which initiates the attachment of inflammatory cells. Peroxisome proliferator-activated receptor (PPAR)-gamma is considered an important immunomodulatory factor as well as a fatty acid regulator. In this study, we researched the expression of PPAR-gamma in renal ischemia-reperfusion injury of the rat. The right kidney was harvested and left renal artery and vein were clamped under laparotomy. The kidney was reperfused after 90 minutes of ischemia, and rats were sacrificed at 0, 1.5, 3, 5, 12, and 24 hours after reperfusion. PPAR-gamma expression was analyzed by immunohistochemical staining using monoclonal antibody. In normal kidney, PPAR-gamma staining was weak on endothelial cells, including mesangial cells. On the other hand, PPAR-gamma staining was weak on interstitial cells and strong on collecting ducts of medulla. From 1.5 to 5 hours after reperfusion, PPAR-gamma staining was strong on endothelial cells, moderate on interstitial cells, and strong on collecting ducts. Twelve hours after reperfusion, PPAR-gamma staining was weak on endothelial cells, moderate on interstitial cells, and strong on collecting ducts. PPAR-gamma is induced on collecting ducts, interstitial cells, and endothelial cells in a rat model having renal ischemia-reperfusion injury.

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

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

Inhibition of IL-10-induced STAT3 activation by 15-deoxy-Δ12,14-prostaglandin J2

OBJECTIVES

15-Deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) is a natural ligand that activates the peroxisome proliferator-activated receptor (PPAR)-gamma, a member of the nuclear receptor family implicated in the regulation of lipid metabolism and adipocyte differentiation. Recent data have shown that 15d-PGJ2 exerts anti-inflammatory action via inhibition of the interferon gamma (IFN-gamma)-induced Jak-STAT signalling pathway. The anti-inflammatory effect of IL-10 is mediated via activated STAT3 (signal transducer and activator of transcription 3). In this study, we investigated whether 15d-PGJ2 inhibit IL-10-induced STAT activation.

METHODS

We used western blotting, flow cytometric analysis and a real-time polymerase chain reaction.

RESULTS

15d-PGJ2 blocked IL-10-induced STAT1 and STAT3 activation in primary human monocytes, macrophages and THP-1 cells. Inhibition was not specific for IL-10, as induction of STAT activation by IFN-gamma and IL-6 was also inhibited by 15d-PGJ2. Inhibition of IL-10 signalling was induced within 1 h after pretreatment of 15d-PGJ2. Other PPARgamma agonists, such as troglitazone, did not inhibit IL-10 signalling. Treatment with GW9662, a specific PPARgamma antagonist, had no effect on 15d-PGJ2-mediated inhibition of IL-10 signalling even at higher concentrations (50 microM), indicating that 15d-PGJ2 affects the IL-10-induced Jak-STAT signalling pathway via an PPARgamma-independent mechanism. Actinomycin D had no effect on 15d-PGJ2-mediated inhibition of IL-10 signalling, indicating that inhibition of IL-10 signalling occurs independently of de novo gene expression. Also, inhibitors of extracellular signal-regulated kinase (ERKs) (PD98059), p38 MAPK (mitogen-activated protein kinase) (SB203580) and protein kinase C (PKC) (GF109203X, calphostin C) had no effect on 15d-PGJ2-mediated inhibition of IL-10 signalling. These results show that MAPKs and PKC are not involved in the inhibition of IL-10 signalling.

CONCLUSIONS

We showed that 15d-PGJ2 non-specifically inhibits STAT signalling of the anti-inflammatory cytokine IL-10 as well as the proinflammatory cytokine IFN-gamma. These findings indicate the possibility that 15d-PGJ2 can have adverse effects in the management of diseases in which IL-10 plays a critical role in the suppression of inflammation.

Cardioprotective effects of peroxisome proliferator activated receptor gamma activators on acute myocarditis: anti-inflammatory actions associated with nuclear factor kappaB blockade

OBJECTIVE

To test the hypothesis that activation of peroxisome proliferator activated receptor gamma (PPAR-gamma) reduces experimental autoimmune myocarditis (EAM) associated with inhibitor kappaB (IkappaB) alpha induction, blockade of nuclear factor kappaB (NF-kappaB), and inhibition of inflammatory cytokine expression.

METHODS

EAM was induced in Lewis rats by immunisation with porcine cardiac myosin. PPAR-gamma activators 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) and pioglitazone (PIO) were administered to rats with EAM.

RESULTS

Enhanced PPAR-gamma expression was prominently stained in the nuclear and perinuclear regions of infiltrating inflammatory cells. Administration of 15d-PGJ2 and PIO greatly reduced the severity of myocarditis and suppressed myocardial mRNA and protein expression of inflammatory cytokines in rats with EAM. In addition, treatment with PPAR-gamma activators enhanced IkappaB concentrations in the cytoplasmic fractions and nuclear fractions from inflammatory myocardium. Concurrently, NF-kappaB was greatly activated in myocarditis; this activation was blocked in the 15d-PGJ2 treated and PIO treated groups.

CONCLUSIONS

PPAR-gamma may have a role in the pathophysiology of EAM. Because an increase in IkappaB expression and inhibition of translocation of the NF-kappaB subunit p65 to the nucleus in inflammatory cells correlated with the protective effects of PPAR-gamma activators, these results suggest that PPAR-gamma activators act sequentially through PPAR-gamma activation, IkappaB induction, blockade of NF-kappaB activation, and inhibition of inflammatory cytokine expression. These results suggest that PPAR-gamma activators such as 15d-PGJ2 and PIO may have the potential to modulate human inflammatory heart diseases such as myocarditis.

Pioglitazone, a peroxisome proliferator-activated receptor gamma agonist, reduces the progression of experimental osteoarthritis in guinea pigs

OBJECTIVE

To evaluate the in vivo therapeutic effect of pioglitazone, a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, on the development of lesions in a guinea pig model of osteoarthritis (OA), and to determine the influence of pioglitazone on the synthesis of matrix metalloproteinase 13 (MMP-13) and interleukin-1beta (IL-1beta) in articular cartilage.

METHODS

The OA model was created by partial medial meniscectomy of the right knee joint. The guinea pigs were divided into 4 treatment groups: unoperated animals that received no treatment (normal), operated animals (OA guinea pigs) that received placebo, OA guinea pigs that received oral pioglitazone at 2 mg/kg/day, and OA guinea pigs that received oral pioglitazone at 20 mg/kg/day. The animals began receiving medication 1 day after surgery and were killed 4 weeks later. Macroscopic and histologic analyses were performed on the cartilage. The levels of MMP-13 and IL-1beta in OA cartilage chondrocytes were evaluated by immunohistochemistry.

RESULTS

OA guinea pigs treated with the highest dosages of pioglitazone showed a significant decrease, compared with the OA placebo group, in the surface area (size) and grade (depth) of cartilage macroscopic lesions on the tibial plateaus. The histologic severity of cartilage lesions was also reduced. A significantly higher percentage of chondrocytes in the middle and deep layers stained positive for MMP-13 and IL-1beta in cartilage from placebo-treated OA guinea pigs compared with normal controls. Guinea pigs treated with the highest dosage of pioglitazone demonstrated a significant reduction in the levels of both MMP-13 and IL-1beta in OA cartilage.

CONCLUSION

This is the first in vivo study demonstrating that a PPARgamma agonist, pioglitazone, could reduce the severity of experimental OA. This effect was associated with a reduction in the levels of MMP-13 and IL-1beta, which are known to play an important role in the pathophysiology of OA lesions.

15d-PGJ2: the anti-inflammatory prostaglandin?

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

15d-prostaglandin J2 reduces multiple organ failure caused by wall-fragment of Gram-positive and Gram-negative bacteria

Septic shock is still the major cause of death in surgical intensive care units. Both gram-positive (G+) and gram-negative (G-) bacteria have been isolated in the blood of a large portion of septic patients, and these polymicrobial infections often have a higher mortality than infections due to a single organism. Cell wall fragments from G+ and G- bacteria synergise to cause shock and multiple organ dysfunction in vivo (G+/G- shock). Male Wistar rats were anaesthetised and received a coadministration of wall fragments from G+ and G- bacteria, Staphilococcus aureus (S. aureus) peptidoglycan [0.3 mg/kg, intravenously (i.v.)] and Escherichia coli (E. coli) lipopolysaccharide (1 mg/kg, i.v.) or vehicle (saline, 1 ml/kg, i.v.). G+/G- shock for 6 h resulted in an increase in serum levels of creatinine (indicator of renal dysfunction), alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transferase (gamma-GT), bilirubin (markers for hepatic injury and dysfunction) and creatine kinase (CK, an indicator of neuromuscular, skeletal muscle or cardiac injury). Pretreatment of rats with the peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist 15d-prostaglandin J2 (0.3 mg/kg, i.v., 30 min prior to G+/G-) reduced the multiple organ injury/dysfunction caused by coadministration of peptidoglycan+lipopolysaccharide. The selective PPAR-gamma antagonist GW9662 (2-Chloro-5-nitrobenzanilide) (1 mg/kg, i.v., given 45 min prior to G+/G-) abolished the protective effects of 15d-prostaglandin J2. 15d- prostaglandin J2 did not affect the biphasic fall in blood pressure or the increase in heart rate caused by administration of peptidoglycan+lipopolysaccharide. The mechanism(s) of the protective effect of this cyclopentenone prostaglandin are-at least in part-PPAR-gamma dependent, as the protection afforded by 15d-prostaglandin J2 was reduced by the PPAR-gamma antagonist GW9662. We propose that 15d-prostaglandin J2 or other ligands for PPAR-gamma may be useful in the therapy of the organ injury associated with septic shock.

COX expression and PGE2 and PGD2 production in experimental acute and chronic gastric lesions

Prostaglandin E(2) and D(2) (PGE(2) and PGD(2)) production and cyclooxygenase-2 (COX-2) expression during the resolution of acute and chronic gastric inflammatory lesions in Wistar rats have been investigated. Differences between ibuprofen, nonselective COX inhibitor, and rofecoxib, specific COX-2 inhibitor, on the development of the induced responses were also analysed. In an acute model, by instillation of HCL, the greatest injury was observed early with a rapid and progressive restoration. Maximal up-regulation of COX-2 protein was detected at 6 h and was accompanied by increase of PGE(2) synthesis but not PGD(2). Both drugs stimulated COX-2 expression in accordance to their capacity of inhibiting this enzymatic activity, driving to delay in the healing. In a chronic model, by acetic acid-induced gastric ulcers, COX-2 was expressed at 7 days and was also associated with PGE(2) increase. Ibuprofen and rofecoxib also augmented COX-2 protein and inhibited PGE(2) levels. However, PGD(2) production was augmented when none signal of COX-2 protein could be detected. Together, this study confirms the role played by COX-2 enzyme in the resolution of acute and chronic gastric inflammatory process, PGE(2) being the principal product. The antiinflammatory effect of nonsteroidal antiinflammatory drugs (NSAIDs) could be mediated not only through the inhibition of COX activity but also through the induction of antiinflammatory PGs production-such as PGD(2)-although further studies would be needed to clarify the mechanisms of this activity and the possible implicated processes.

The fatty acid-binding protein, aP2, coordinates macrophage cholesterol trafficking and inflammatory activity. Macrophage expression of aP2 impacts peroxisome proliferator-activated receptor gamma and IkappaB kinase activities

Fatty acid-binding proteins are cytosolic fatty acid chaperones, and the adipocyte isoform, aP2, plays an important role in obesity and glucose metabolism. Recently, this protein has been detected in macrophages where it strongly contributes to the development of atherosclerosis. Here, we investigated the role of aP2 in macrophage biology and the molecular mechanisms underlying its actions. We demonstrate that aP2-deficient macrophages display defects in cholesterol accumulation and alterations in pro-inflammatory responsiveness. Deficiency of aP2 alters the lipid composition in macrophages and enhances peroxisome proliferator-activated receptor gamma activity, leading to elevated CD36 expression and enhanced uptake of modified low density lipoprotein. The increased peroxisome proliferator-activated receptor gamma activity in aP2-deficient macrophages is also accompanied by a significant stimulation of the liver X receptor alpha-ATP-binding cassette transporter A1-mediated cholesterol efflux pathway. In parallel, aP2-deficient macrophages display reduced IkappaB kinase and NF-kappaB activity, resulting in suppression of inflammatory function including reduced cyclooxygenase-2 and inducible nitric-oxide synthase expression and impaired production of inflammatory cytokines. Our results demonstrate that aP2 regulates two central molecular pathways to coordinate macrophage cholesterol trafficking and inflammatory activity.

Peroxisome proliferator-activated receptor-γ ligands reduce inflammation and infarction size in transient focal ischemia

Newly developed insulin-sensitizing agents, which target the nuclear receptor peroxisome proliferator-activated receptor-gamma have recently been appreciated to exhibit potent anti-inflammatory actions. Since stroke is associated with an intense inflammatory response, we reasoned that these agents may ameliorate injury from stroke. We report that administration of troglitazone or pioglitazone 24 h before and at the time of cerebral infarction dramatically reduced infarction volume and improved neurological function following middle cerebral artery occlusion in rats. Furthermore, we find that delayed therapy also significantly reduced infarct volume. The brains of the drug-treated animals displayed reduced inflammation as evidenced by decreased immunoreactivity for microglial/macrophage markers and reduced protein and mRNA for interleukin-1beta, cyclooxygenase-2 and inducible nitric oxide synthase. We argue that the beneficial effects of these drugs are likely due to reduced expression of these inflammatory mediators, which are known to exacerbate ischemic injury following stroke. These results are of particular relevance to diabetic patients chronically treated with these agents who may benefit from the neuroprotective actions of these drugs.

Peroxisome proliferation-activated receptor (PPAR)gamma is not necessary for synthetic PPARgamma agonist inhibition of inducible nitric-oxide synthase and nitric oxide

Peroxisome proliferation-activated receptor (PPAR)gamma agonists inhibit inducible nitric-oxide synthase (iNOS), tumor necrosis factor-alpha, and interleukin-6. Because of these effects, synthetic PPARgamma agonists, including thiazolidinediones, are being studied for their impact on inflammatory disease. The anti-inflammatory concentrations of synthetic PPARgamma agonists range from 10 to 50 microM, whereas their binding affinity for PPARgamma is in the nanomolar range. The specificity of synthetic PPARgamma agonists for PPARgamma at the concentrations necessary for anti-inflammatory effects is thus in question. We report that PPARgamma is not necessary for the inhibition of iNOS by synthetic PPARgamma agonists. RAW 264.7 macrophages possess little PPARgamma, yet lipopolysaccharide (LPS)/interferon (IFN)gamma-induced iNOS was inhibited by synthetic PPARgamma agonists at 20 microM. Endogenous PPARgamma was inhibited by the transfection of a dominant-negative PPARgamma construct into murine mesangial cells. In the transfected cells, synthetic PPARgamma agonists inhibited iNOS production at 10 microM, similar to nontransfected cells. Using cells from PPARgamma Cre/lox conditional knockout mice, baseline and LPS/IFNgamma-induced nitric oxide levels were higher in macrophages lacking PPARgamma versus controls. However, synthetic PPARgamma agonists inhibited iNOS at 10 microM in the PPARgamma-deficient cells, similar to macrophages from wild-type mice. These results indicate that PPARgamma is not necessary for inhibition of iNOS expression by synthetic PPARgamma agonists at concentrations over 10 microM. Intrinsic PPARgamma function, in the absence of synthetic agonists, however, may play a role in inflammatory modulation.

Inhibition of interleukin-1?-induced cyclooxygenase 2 expression in human synovial fibroblasts by 15-deoxy-?12,14-prostaglandin J2 through a histone deacetylase-independent mechanism

OBJECTIVE

The cyclooxygenase (COX) metabolite, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), has been reported to inhibit the expression of a number of genes involved in the pathogenesis of arthritis. However, its effects on COX-2 remain controversial. We undertook this study to investigate the effects of 15d-PGJ(2) on interleukin-1beta (IL-1beta)-induced COX-2 expression in human synovial fibroblasts (HSFs).

METHODS

HSFs were cultured with IL-1beta in the absence or presence of 15d-PGJ(2), and the levels of COX-2 protein and messenger RNA (mRNA) expression were evaluated using Western blotting and real-time reverse transcriptase-polymerase chain reaction, respectively. COX-2 promoter activity was analyzed in transient transfection experiments. Chromatin immunoprecipitation assays were performed to evaluate the level of histone acetylation and the recruitment of histone deacetylases (HDACs) 1, 2, and 3 and histone acetylase (HAT) p300 to the COX-2 promoter.

RESULTS

IL-1beta-induced COX-2 protein and mRNA expression, as well as COX-2 promoter activation, were inhibited by 15d-PGJ(2). Troglitazone, a selective peroxisome proliferator-activated receptor gamma (PPARgamma) ligand, enhanced COX-2 expression, while GW9662, a specific PPARgamma antagonist, relieved the suppressive effect of 15d-PGJ(2). IL-1beta-induced histone H3 acetylation was selectively blocked by 15d-PGJ(2). The reduction of histone H3 acetylation did not correlate with the recruitment of HDACs to the COX-2 promoter. Also, treatment with the specific HDAC inhibitor, trichostatin A, did not relieve the suppressive effect of 15d-PGJ(2), indicating that HDACs are not involved in the inhibitory effect of 15d-PGJ(2). Furthermore, 15d-PGJ(2) blocked IL-1beta-induced recruitment of p300 to the COX-2 promoter, which may be the mechanism for decreased histone H3 acetylation and COX-2 expression. In accordance with this, overexpression of p300, but not of a mutant p300 lacking HAT activity, relieved the inhibitory effect of 15d-PGJ(2) on COX-2 promoter activation.

CONCLUSION

These data suggest that 15d-PGJ(2) can inhibit IL-1beta-induced COX-2 expression by an HDAC-independent mechanism, probably by interfering with HAT p300.

Pro-inflammatory properties for thiazolidinediones

Thiazolidinediones (TZDs) are pharmacological ligands of the peroxisome proliferator-activated receptor (PPAR)-gamma that are extensively used in the treatment of type II diabetes. Recently, an anti-inflammatory potential for TZDs has been suggested, based on observations that these compounds may inhibit pro-inflammatory cytokine expression in vitro and may attenuate the inflammatory response in vivo. Here, we show that the TZDs rosiglitazone (RSG) and troglitazone (TRO) do not inhibit the inflammatory response to tumor necrosis factor (TNF)-alpha in various epithelial cell types. On the contrary, both RSG and TRO significantly potentiated TNF-alpha-induced production of granulocyte/macrophage-colony-stimulating factor, interleukin (IL)-6 and/or IL-8 in these cells. This increase in pro-inflammatory cytokine expression was functionally significant as supernatants from cells co-treated with TNF-alpha and TZDs displayed increased neutrophil pro-survival activity when compared with supernatants from cells treated with TNF-alpha alone. Additionally, it was shown that TZDs enhance cytokine expression at the transcriptional level, but that the pro-inflammatory effects of TZDs are independent on PPARgamma, nuclear factor kappaB or mitogen-activated protein kinase activation. Our study shows that TZDs may potentiate the inflammatory response in epithelial cells, a previously unappreciated effect of these compounds.

Repression of IFN-gamma expression by peroxisome proliferator-activated receptor gamma

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors expressed in a wide variety of cells. Our studies and others have demonstrated that both human and murine T cells express PPARgamma and that expression can be augmented over time in mitogen-activated splenocytes. PPARgamma ligands decrease proliferation and IL-2 production, and induce apoptosis in both B and T cells. PPARgamma ligands have also been shown to be anti-inflammatory in multiple models of inflammatory disease. In the following study, we demonstrate for the first time that PPARgamma is expressed in both murine CD4 and CD8 cells and that PPARgamma ligands directly decrease IFN-gamma expression by murine and transformed T cell lines. Unexpectedly, GW9662, a PPARgamma antagonist, increases lymphocyte IFN-gamma expression. Transient transfection studies reveal that PPARgamma ligands, in a PPARgamma-dependent manner, potently repress an IFN-gamma promoter construct. Repression localizes to the distal conserved sequence of the IFN-gamma promoter. Our studies also demonstrate that PPARgamma acts on the IFN-gamma promoter by interfering with c-Jun activation. These studies suggest that many of the observed anti-inflammatory effects of PPARgamma ligands may be related to direct inhibition of IFN-gamma by PPARgamma.