Peroxisome Proliferation-Activated Receptor (PPAR)γ Is Not Necessary for Synthetic PPARγ Agonist Inhibition of Inducible Nitric-Oxide Synthase and Nitric Oxide

Insulin Sensitizing Pharmacology of Thiazolidinediones Correlates with Mitochondrial Gene Expression rather than Activation of PPARγ

Insulin sensitizing thiazolidinediones (TZDs) are generally considered to work as agonists for the nuclear receptor peroxisome proliferative activated receptor-gamma (PPARγ). However, TZDs also have acute, non-genomic metabolic effects and it is unclear which actions are responsible for the beneficial pharmacology of these compounds. We have taken advantage of an analog, based on the metabolism of pioglitazone, which has much reduced ability to activate PPARγ. This analog (PNU-91325) was compared to rosiglitazone, the most potent PPARγ activator approved for human use, in a variety of studies both in vitro and in vivo. The data demonstrate that PNU-91325 is indeed much less effective than rosiglitazone at activating PPARγ both in vitro and in vivo. In contrast, both compounds bound similarly to a mitochondrial binding site and acutely activated PI-3 kinase-directed phosphorylation of AKT, an action that was not affected by elimination of PPARγ activation. The two compounds were then compared in vivo in both normal C57 mice and diabetic KKAy mice to determine whether their pharmacology correlated with biomarkers of PPARγ activation or with the expression of other gene transcripts. As expected from previous studies, both compounds improved insulin sensitivity in the diabetic mice, and this occurred in spite of the fact that there was little increase in expression of the classic PPARγ target biomarker adipocyte binding protein-2 (aP2) with PNU-91325 under these conditions. An examination of transcriptional profiling of key target tissues from mice treated for one week with both compounds demonstrated that the relative pharmacology of the two thiazolidinediones correlated best with an increased expression of an array of mitochondrial proteins and with expression of PPARγ coactivator 1-alpha (PGC1α), the master regulator of mitochondrial biogenesis. Thus, important pharmacology of the insulin sensitizing TZDs may involve acute actions, perhaps on the mitochondria, that are independent of direct activation of the nuclear receptor PPARγ. These findings suggest a potential alternative route to the discovery of novel insulin sensitizing drugs.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

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

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

Structural properties of silver doped hydroxyapatite and their biocompatibility

The aim of this study was to obtain a novel hydroxyapatite-based material with high biocompatibility. The structural properties of the samples were well characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The X-ray diffraction studies revealed the characteristic peaks of hydroxyapatite in each sample. Other phases or impurities were not observed. The scanning electron microscopy observations suggest that the doping components have no influence on the surface morphology of the samples, which reveals a homogeneous aspect of the synthesized particles for all samples. The presence of calcium (Ca), phosphor (P), oxygen (O) and silver (Ag) in the Ag:HAp is confirmed by energy dispersive X-ray (EDAX) and X-ray Photoelectron Spectroscopy analyses. Nanocrystalline silver doped HAp stimulated viability and potentiated the activation of murine macrophages.

Peptidoglycan induced expression of peroxisome proliferator-activated receptor γ in mouse peritoneal macrophages: role of ERK and JNK MAP kinases

The peroxisome proliferator-activated receptor (PPAR) γ plays an important role in macrophage inflammatory homeostasis. Here we investigate the cross talk between PPARγ and TLR2 signaling pathway in mouse peritoneal macrophages. Real time RT-PCR and immunoblot analysis revealed that peptidoglycan (PGN) treatment of macrophages leads to biphasic effect on PPARγ expression i.e. an early upregulation and a late suppression. Inhibition of ERK MAP kinase by PD98059 abolished the early and rapid induction of PPARγ, while the inhibition of JNK MAP kinase by SP600125 nullifies the late inhibitory effect on the PPARγ expression in a dose-dependent manner. Furthermore, PPARγ knockdown macrophages showed enhanced NF-κB activity after PGN treatment. PGN treatment also enhances PPARγ interaction with p65 as observed by immunoprecipitation. This interaction may inhibit NF-κB (p65) activity as increased nuclear localization of p65 was observed in PPARγ knockdown macrophages after PGN treatment. PPARγ knockdown also increased the PGN-induced inflammatory cytokines (TNF-α, IL-1β, IL-12p40) production. Thus, our observations suggest that PGN induces PPARγ expression which is regulated by MAPKs activation and this enhanced PPARγ in turn attenuate NF-κB activity probably via enhancing p65 nuclear export. These results provide insight into how these pathways could be modulated in inflammatory diseases.

Rosiglitazone regulates c-reactive protein-induced inflammatory responses via glucocorticoid receptor-mediated inhibition of p38 mitogen-activated protein kinase-toll-like receptor 4 signal pathway in vascular smooth muscle cells

C-reactive protein (CRP) activates toll-like receptor 4 (TLR4) to initiate inflammatory response involved in the pathogenesis of atherosclerosis through mitogen-activated protein kinase (MAPK) signal pathways. Rosiglitazone, a synthetic peroxisome proliferator-activated receptor γ (PPARγ) agonist, is considered to be an important inhibitor of the inflammatory response. The present study was to explore the effect of rosiglitazone on the CRP-induced inflammatory responses and the related signal pathway in vascular smooth muscle cells (VSMCs). The results showed that rosiglitazone reduced the expressions of proinflammatory cytokines, such as vascular endothelial growth factor-A and inducible nitric oxide synthase, and enhanced the expression or activation of anti-inflammatory transcription factors including PPARγ and glucocorticoid receptor (GR) in VSMCs in response to CRP. The further investigations indicated that rosiglitazone inhibited CRP-induced TLR4 expression and p38 MAPK phosphorylation in VSMCs, and TLR4 knockdown potentiated the inhibitory effects of rosiglitazone on vascular endothelial growth factor-A and inducible nitric oxide synthase expressions. In addition, GR antagonist RU486 but not PPARγ inhibitor GW9662 remarkably weakened the inhibitory effects of rosiglitazone on CRP-induced TLR4 expression and p38 phosphorylation in VSMCs. But GW9662 did not affect rosiglitazone-induced GR phosphorylation. These suggest that rosiglitazone exerts its anti-inflammatory effect through activating GR and subsequently inhibiting p38 MAPK-TLR4 signaling pathway in CRP-stimulated VSMCs.

Pathophysiological Roles of PPARgamma in Gastrointestinal Epithelial Cells

Although the highest levels of PPARγ expression in the body have been reported in the gastrointestinal epithelium, little is known about the physiological functions of that receptor in the gut. Moreover, there is considerable controversy concerning the effects of thiazolidinedione PPARγ agonists on the two major diseases of the gastrointestinal track: colorectal cancer and inflammatory bowel disease. We will undertake to review both historical and recently published data with a view toward summarizing what is presently known about the roles of PPARγ in both physiological and pathological processes in the gastrointestinal epithelium.

Synthesis and biological evaluation of novel 5-benzylidenethiazolidine-2,4-dione derivatives for the treatment of inflammatory diseases

Twenty-two compounds based on thiazolidine-2,4-dione moiety were synthesized and evaluated for the inhibitory potency on the production of nitric oxide (NO), inducible nitric oxide synthase (iNOS) activity, and the generation of prostaglandin E(2) (PEG(2)). (Z)-N-(3-chlorophenyl)-2-(4-((2,4-dioxothiazolidin-5-ylidene) methyl) phenoxy) acetamide (3I), superior to the commercial anti-inflammatory drug indomethacin, significantly inhibited iNOS activity (IC(50) = 8.66 μM), iNOS-mediated NO, and cyclooxygenase (COX)-2-derived PGE(2) production (IC(50) = 4.16 and 23.55 μM, respectively) on lipopolysaccharide (LPS)-induced RAW 264.7 cells. Docking study revealed that 3I was perfectly docking into the active site of murine iNOS and suppressed the expression of iNOS protein as evidenced by Western blot analysis. At the dose of 50 mg/kg, oral administration of 3I possessed protective properties in both carrageenan-induced paw edema and adjuvant-induced arthritis rat models.

Abscisic acid regulates inflammation via ligand-binding domain-independent activation of peroxisome proliferator-activated receptor gamma

Abscisic acid (ABA) has shown efficacy in the treatment of diabetes and inflammation; however, its molecular targets and the mechanisms of action underlying its immunomodulatory effects remain unclear. This study investigates the role of peroxisome proliferator-activated receptor γ (PPAR γ) and lanthionine synthetase C-like 2 (LANCL2) as molecular targets for ABA. We demonstrate that ABA increases PPAR γ reporter activity in RAW 264.7 macrophages and increases ppar γ expression in vivo, although it does not bind to the ligand-binding domain of PPAR γ. LANCL2 knockdown studies provide evidence that ABA-mediated activation of macrophage PPAR γ is dependent on lancl2 expression. Consistent with the association of LANCL2 with G proteins, we provide evidence that ABA increases cAMP accumulation in immune cells. ABA suppresses LPS-induced prostaglandin E(2) and MCP-1 production via a PPAR γ-dependent mechanism possibly involving activation of PPAR γ and suppression of NF-κB and nuclear factor of activated T cells. LPS challenge studies in PPAR γ-expressing and immune cell-specific PPAR γ null mice demonstrate that ABA down-regulates toll-like receptor 4 expression in macrophages and T cells in vivo through a PPAR γ-dependent mechanism. Global transcriptomic profiling and confirmatory quantitative RT-PCR suggest novel candidate targets and demonstrate that ABA treatment mitigates the effect of LPS on the expression of genes involved in inflammation, metabolism, and cell signaling, in part, through PPAR γ. In conclusion, ABA decreases LPS-mediated inflammation and regulates innate immune responses through a bifurcating pathway involving LANCL2 and an alternative, ligand-binding domain-independent mechanism of PPAR γ activation.

Long chain acyl-CoA synthetase-3 is a molecular target for peroxisome proliferator-activated receptor delta in HepG2 hepatoma cells

ACSL3 is a member of the long chain acyl-CoA synthetase (ACSL) family that plays key roles in fatty acid metabolism in various tissues in an isozyme-specific manner. Our previous studies showed that ACSL3 was transcriptionally up-regulated by the cytokine oncostatin M (OSM) in HepG2 cells, accompanied by reduced cellular triglyceride content and enhanced beta-oxidation. In this study, we investigated the molecular mechanism underlying the OSM-induced activation of ACSL3 gene transcription in HepG2 cells. We showed that OSM treatment resulted in a coordinated elevation of mRNA levels of ACSL3 and peroxisome proliferator-activated receptor delta (PPARdelta). The effect of OSM on ACSL3 mRNA expression was inhibited by cellular depletion of PPARdelta. By utilizing a PPARdelta agonist, L165041, we demonstrated that activation of PPARdelta led to increases in ACSL3 promoter activity, mRNA level, and protein level in HepG2 cells. Analysis of the ACSL3 promoter sequence identified two imperfect PPAR-responsive elements (PPRE) located in the ACSL3 promoter region -944 to -915, relative to the transcription start site. The up-regulation of ACSL3 promoter activity by PPARdelta was abolished by deletion of this PPRE-containing region or mutation to disrupt the binding sites. Direct interactions of PPARdelta with ACSL3-PPRE sequences were demonstrated by gel mobility shift and chromatin immunoprecipitation assays. Finally, we provided in vivo evidence showing that activation of PPARdelta by L165041 in hamsters increased ACSL3 mRNA and protein levels in the liver. These new findings define ACSL3 as a novel molecular target of PPARdelta in HepG2 cells and provide a regulatory mechanism for ACSL3 transcription in liver tissue.

Treatment with a peroxisomal proliferator activated receptor gamma agonist has a modest effect in the allergen challenge model in asthma: a randomised controlled trial

PURPOSE

A considerable body of non clinical evidence has accumulated to support peroxisomal proliferator-activated receptor gamma agonists as candidate anti-inflammatory drugs in asthma. We utilized rosiglitazone as a tool compound in the inhaled allergen challenge model of asthma.

METHODS

A single centre, double-blind, randomised, placebo controlled, two period cross-over study. Subjects received rosiglitazone 4mg and placebo twice daily for 28 days in random order. On day 28, inhaled allergen challenge was performed 1 hour post-dose. A methacholine challenge was performed on day 29 and an adenosine monophosphate challenge on day 14. Exhaled nitric oxide was measured on days 1, 14, 28, 29. Blood was collected pre dose on days 1, 14 and 28 and analysed for markers associated with PPAR activity and systemic markers of inflammation.

RESULTS

The late asthmatic reaction (LAR) change from post saline FEV(1) from 4-10 hrs post allergen on day 28 was statistically significant for the weighted mean LAR. The difference in weighted mean was 0.06 L (95% CI 0.01 to 0.11) which equates to a 15% attenuation of the response during placebo treatment. This was accompanied by trends in other markers of efficacy and anti-inflammatory activity but none were considered major effects.

DISCUSSION

Treatment with a PPARgamma agonist (rosiglitazone) was associated with a modest (15%) reduction in the late asthmatic reaction in the allergen challenge model of asthma. Based on the results of this study, PPARgamma agonist monotherapy is unlikely to represent a clinically useful intervention in human asthma. Registered with www.clinicaltrials.gov (NCT00318630).

PPARs in Irradiation-Induced Gastrointestinal Toxicity

The use of radiation therapy to treat cancer inevitably involves exposure of normal tissues. Although the benefits of this treatment are well established, many patients experience distressing complications due to injury to normal tissue. These side effects are related to inflammatory processes, and they decrease therapeutic benefit by increasing the overall treatment time. Emerging evidence indicates that PPARs and their ligands are important in the modulation of immune and inflammatory reactions. This paper discusses the effects of abdominal irradiation on PPARs, their role and functions in irradiation toxicity, and the possibility of using their ligands for radioprotection.

Pioglitazone protects the myocardium against ischemia-reperfusion injury in eNOS and iNOS knockout mice

Endothelial nitric oxide synthase (eNOS) activation with subsequent inducible NOS (iNOS), cytosolic phospholipase A2 (cPLA2), and cyclooxygenase-2 (COX2) activation is essential to statin inhibition of myocardial infarct size (IS). In the rat, the peroxisome proliferator-activated receptor-gamma agonist pioglitazone (Pio) limits IS, upregulates and activates cPLA2 and COX2, and increases myocardial 6-keto-PGF1alpha levels without activating eNOS and iNOS. We asked whether Pio also limits IS in eNOS-/- and iNOS-/- mice. Male C57BL/6 wild-type (WT), eNOS-/-, and iNOS-/- mice received 10 mg.kg(-1).day(-1) Pio (Pio+) or water alone (Pio-) for 3 days. Mice underwent 30 min coronary artery occlusion and 4 h reperfusion, or hearts were harvested and subjected to ELISA and immunoblotting. As a result, Pio reduced IS in the WT (15.4+/-1.4% vs. 39.0+/-1.1%; P<0.001), as well as in the eNOS-/- (32.0+/-1.6% vs. 44.2+/-1.9%; P<0.001) and iNOS-/- (18.0+/-1.2% vs. 45.5+/-2.3%; P<0.001) mice. The protective effect of Pio in eNOS-/- mice was smaller than in the WT (P<0.001) and iNOS-/- (P<0.001) mice. Pio increased myocardial Ser633 and Ser1177 phosphorylated eNOS levels in the WT and iNOS-/- mice. iNOS was undetectable in all six groups. Pio increased cPLA2, COX2, and PGI2 synthase levels in the WT, as well as in the eNOS-/- and iNOS-/-, mice. Pio increased the myocardial 6-keto-PGF1alpha levels and cPLA2 and COX2 activity in the WT, eNOS-/-, and iNOS-/- mice. In conclusion, the myocardial protective effect of Pio is iNOS independent and may be only partially dependent on eNOS. Because eNOS activity decreases with age, diabetes, and advanced atherosclerosis, this effect may be relevant in a clinical setting and should be further characterized.

Peroxisome proliferator-activated receptor gamma down-regulates follistatin in intestinal epithelial cells through SP1

Activation of peroxisome proliferator-activated receptor gamma (PPARgamma) down-regulates the expression of follistatin mRNA in intestinal epithelial cells in vivo. The mechanism of PPARgamma-mediated down-regulation of follistatin was investigated using non-transformed, rat intestinal epithelial cells (RIE-1). RIE cells expressed activin A, the activin receptors ActRI and ActRII, and the follistatin-315 mRNA. RIE-1 cells responded to endogenous activin A, and this response was antagonized by follistatin, as evidenced by changes in cell growth and regulation of an activin-responsive reporter. Using RIE-1 cells, we show that activation of PPARgamma by rosiglitazone reduced follistatin mRNA levels in a dose- and concentration-dependent manner. Down-regulation of follistatin by rosiglitazone required the DNA binding domain of PPARgamma and was dependent upon dimerization with the retinoid X receptor. Inhibition of follistatin expression by rosiglitazone was not associated with decreased follistatin mRNA stability, suggesting that regulation may be at the promoter level. Analysis of the follistatin promoter revealed consensus binding sites for AP-1, AP-2, and Sp1. Targeting the AP-1 pathway with SP600125, an inhibitor of JNK, and TAM67, a dominant negative c-Jun, had no effect on PPARgamma-mediated down-regulation of follistatin. However, the follistatin promoter was dramatically regulated by Sp1, and this regulation was inhibited by PPARgamma expression. Knockdown of Sp1 expression relieved repression of follistatin levels by rosiglitazone. Moreover, PPARgamma was found to interact with Sp1 and repress its transcriptional activation function. Collectively, our data indicate that repression of Sp1 transcriptional activity by PPARgamma is the underlying mechanism responsible for PPARgamma-mediated regulation of follistatin expression.

Toll-like receptor 4 mediates cross-talk between peroxisome proliferator-activated receptor gamma and nuclear factor-kappaB in macrophages

The peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed in macrophages and plays an important role in suppressing the inflammatory response. Lipopolysaccharides (LPS), which activate Toll-like receptor 4 (TLR4), reduced PPARgamma expression and function in peritoneal macrophages and macrophage cell lines. Moreover, pretreatment with the synthetic PPARgamma ligand, rosiglitazone did not prevent LPS-mediated downregulation of PPARgamma. Inhibition of PPARgamma expression was not blocked by cycloheximide, indicating that de novo protein synthesis is not required for LPS-mediated suppression of PPARgamma. Destabilization of PPARgamma messenger RNA (mRNA) was not observed in LPS-stimulated macrophages, suggesting that LPS regulates the synthesis of PPARgamma mRNA. LPS had no effect on PPARgamma expression in macrophages from TLR4 knockout mice, whereas LPS inhibited PPARgamma expression in cells that had been reconstituted to express functional TLR4. Targeting the TLR4 pathway with inhibitors of MEK1/2, p38, JNK and AP-1 had no effect on PPARgamma downregulation by LPS. However, inhibitors that target NEMO, IkappaB and NF-kappaB abolished LPS-mediated downregulation of PPARgamma in LPS-stimulated macrophages. Our data indicate that activation of TLR4 inhibits PPARgamma mRNA synthesis by an NF-kappaB-dependent mechanism. Low-density genomic profiling of macrophage-specific PPARgamma knockout cells indicated that PPARgamma suppresses inflammation under basal conditions, and that loss of PPARgamma expression is sufficient to induce a proinflammatory state. Our data reveal a regulatory feedback loop in which PPARgamma represses NF-kappaB-mediated inflammatory signalling in unstimulated macrophages; however, upon activation of TLR4, NF-kappaB drives down PPARgamma expression and thereby obviates any potential anti-inflammatory effects of PPARgamma in LPS-stimulated macrophages.

Rosiglitazone but not losartan prevents Nrf-2 dependent CD36 gene expression up-regulation in an in vivo atherosclerosis model

Background

Thiazolidinediones exert anti-inflammatory and anti-oxidative roles and attenuate atherosclerosis by mechanisms partially independent of their metabolizing actions. High doses of angiotensin type 1 receptor (AT₁R) blocker losartan (LST) seem to promote fat cell formation by preserving PPARγ activity.

Methods

C57BL/6J diet-induced atherosclerotic susceptible mice randomly received a normal or a high-fat high-cholesterol (HFHC) diet and were treated with rosiglitazone (RG), LST or a vehicle for 12 weeks.

Results

HFHC was associated with increased PPARγ gene expression without an over regulation of PPARγ responsive genes, whereas RG and LST treatments were found to maintain PPARγ activity without resulting in increased PPARγ gene expression. A better anti-inflammatory and antioxidant profile in mice treated with RG regarding LST was observed in spite of a similar PPARγ preserved activity. Chromatin immunoprecipitation (ChIP) assays revealed that animals under HFHC diet treated with RG showed a significant nuclear factor erythroid 2-like 2 (Nrf2)-dependent down-regulation of the expression of the CD36 gene.

Conclusion

The PPARγ agonist RG exerts antioxidant properties that significantly reduced Nrf-2-dependent CD-36 up-regulation in mice under HFHC diet. Because LST treatment was also associated with a preserved PPARγ activity, our data suggests that these RG antioxidant effects are partially independent of its PPARγ metabolizing properties.

Reduction of peroxisome proliferation-activated receptor gamma expression by gamma-irradiation as a mechanism contributing to inflammatory response in rat colon: modulation by the 5-aminosalicylic acid agonist

Radiation-induced intestinal injuries, including inflammation and immune response, remain a limiting factor in the effectiveness of pelvic radiotherapy and in the patient's quality of life during and after treatment. Peroxisome proliferation-activated receptor (PPAR) agonists are now emerging as therapeutic drugs for various inflammatory diseases that are characterized by impaired PPAR expression. The purpose of this study was to investigate the profile of PPAR expression in rat colonic mucosa 3 and 7 days after abdominal gamma-irradiation (10 Gy). We tested whether irradiation-induced acute inflammatory response could be modulated pharmacologically with the antiinflammatory properties of 5-aminosalicylic acid (5-ASA) (250 mg/kg/day), which is a PPAR activator. Irradiation drastically reduced mRNA and protein levels of PPARalpha and -gamma and of the heterodimer retinoid X receptor (RXR)alpha at 3 days postirradiation. 5-ASA treatment normalized both PPARgamma and RXRalpha expression at 3 days postirradiation and PPARalpha at 7 days. By promoting PPAR expression and its nuclear translocation, 5-ASA interfered with the nuclear factor (NF)-kappaB pathway, both by reducing irradiation-induced NF-kappaB p65 translocation/activation and increasing the expression of nuclear factor-kappaB inhibitor (IkappaB) mRNA and protein. Therefore, 5-ASA prevents irradiation-induced inflammatory processes as well as expression of tumor necrosis factor alpha, monocyte chemotactic protein-1, inducible nitric-oxide synthase, and macrophage infiltration. In addition, 5-ASA restores the interferon gamma/signal transducer and activator of transcription (STAT)-1 and STAT-3 concentrations that were impaired at 3 and 7 days postirradiation and are correlated with suppressor of cytokine signaling-3 repression. Collectively, these results indicate that PPAR agonists may be effective in the prevention of inflammatory processes and immune responses during and after pelvic radiotherapy.

Peroxisome proliferator-activated receptor-gamma agonists as potential anti-inflammatory agents in asthma and chronic obstructive pulmonary disease

Inhaled corticosteroids are the most effective therapy for chronic persistent asthma and have a role in the treatment of chronic obstructive pulmonary disease (COPD). However, corticosteroids have reduced efficacy in some patients with asthma and fail to halt the progressive deterioration in lung function characteristic of COPD. Additional or alternative drug treatments to corticosteroids are required to improve control of inflammation in patients with therapy resistant airway disease. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists have displayed potent anti-inflammatory properties in experimental models of asthma and other airway diseases and as a result have the potential to become an additional treatment for asthma and COPD. We review the evidence from these experimental models and their applicability to asthma and COPD and the requirements for future clinical and experimental research.

Regulation of LPS stimulated ROS production in peritoneal macrophages from alloxan-induced diabetic rats: involvement of high glucose and PPARgamma

An increased occurrence of long term bacterial infections is common in diabetic patients. Bacterial cell wall components are described as the main antigenic agents from these microorganisms and high blood glucose levels are suggested to be involved in altered immune response. Hyperglycemia is reported to alter macrophages response to lipopolysaccharide (LPS) and peroxisome proliferators activated receptor gamma (PPARgamma) expression. Additionally, glucose is the main metabolic fuel for reduced nicotinamide adenine dinucleotide phosphate (NADPH) production by pentose phosphate shunt. In this work, lipopolysaccharide (LPS) stimulated reactive oxygen species (ROS) and nitrite production were evaluated in peritoneal macrophages from alloxan-induced diabetic rats. Cytosolic dehydrogenases and PPARgamma expression were also investigated. LPS was ineffective to stimulate ROS and nitrite production in peritoneal macrophages from diabetic rats, which presented increased glucose-6-phosphate dehydrogenase and malate dehydrogenase activity. In RAW 264.7 macrophages, acute high glucose treatment abolished LPS stimulated ROS production, with no effect on nitrite and dehydrogenase activities. Peritoneal macrophages from alloxan-treated rats presented reduced PPARgamma expression. Treating RAW 264.7 macrophages with a PPARgamma antagonist resulted in defective ROS production in response to LPS, however, stimulated nitrite production was unaltered. In conclusion, in the present study we have reported reduced nitric oxide and reactive oxygen species production in LPS-treated peritoneal macrophages from alloxan-induced diabetic rats. The reduced production of reactive oxygen species seems to be dependent on elevated glucose levels and reduced PPARgamma expression.

Regulation of inflammation by PPARs: a future approach to treat lung inflammatory diseases?

Lung inflammatory diseases, such as acute lung injury (ALI), asthma, chronic obstructive pulmonary disease (COPD) and lung fibrosis, represent a major health problem worldwide. Although glucocorticoids are the most potent anti-inflammatory drug in asthma, they exhibit major side effects and have poor activity in lung inflammatory disorders such as ALI or COPD. Therefore, there is growing need for the development of alternative or new therapies to treat inflammation in the lung. Peroxisome proliferator-activated receptors (PPARs), including the three isotypes PPARalpha, PPARbeta (or PPARdelta) and PPARgamma, are transcription factors belonging to the nuclear hormone receptor superfamily. PPARs, and in particular PPARalpha and PPARgamma, are well known for their critical role in the regulation of energy homeostasis by controlling expression of a variety of genes involved in lipid and carbohydrate metabolism. Synthetic ligands of the two receptor isotypes, the fibrates and the thiazolidinediones, are clinically used to treat dyslipidaemia and type 2 diabetes, respectively. Recently however, PPARalpha and PPARgamma have been shown to exert a potent anti-inflammatory activity, mainly through their ability to downregulate pro-inflammatory gene expression and inflammatory cell functions. The present article reviews the current knowledge of the role of PPARalpha and PPARgamma in controlling inflammation, and presents different findings suggesting that PPARalpha and PPARgamma activators may be helpful in the treatment of lung inflammatory diseases.

Regulation of peroxisome proliferator-activated receptor-gamma in liver fibrosis

The peroxisome proliferator-activated receptors (PPARs) impart diverse cellular effects in biological systems. Because stellate cell activation during liver injury is associated with declining PPARgamma expression, we hypothesized that its expression is critical in stellate cell-mediated fibrogenesis. We therefore modulated its expression during liver injury in vivo. PPARgamma was depleted in rat livers by using an adenovirus-Cre recombinase system. PPARgamma was overexpressed by using an additional adenoviral vector (AdPPARgamma). Bile duct ligation was utilized to induce stellate cell activation and liver fibrosis in vivo; phenotypic effects (collagen I, smooth muscle alpha-actin, hydroxyproline content, etc.) were measured. PPARgamma mRNA levels decreased fivefold and PPARgamma protein was undetectable in stellate cells after culture-induced activation. During activation in vivo, collagen accumulation, assessed histomorphometrically and by hydroxyproline content, was significantly increased after PPARgamma depletion compared with controls (1.28 +/- 0.14 vs. 1.89 +/- 0.21 mg/g liver tissue, P < 0.03). In isolated stellate cells, AdPPARgamma overexpression resulted in significantly increased adiponectin mRNA expression and decreased collagen I and smooth muscle alpha-actin mRNA expression compared with controls. During in vivo fibrogenesis, rat livers exposed to AdPPARgamma had significantly less fibrosis than controls. Collagen I and smooth muscle alpha-actin mRNA expression were significantly reduced in AdPPARgamma-infected rats compared with controls (P < 0.05, n = 10). PPARgamma-deficient mice exhibited enhanced fibrogenesis after liver injury, whereas PPARgamma receptor overexpression in vivo attenuated stellate cell activation and fibrosis. The data highlight a critical role for PPARgamma during in vivo fibrogenesis and emphasize the importance of the PPARgamma pathway in stellate cells during liver injury.

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.

Augmentation of myocardial production of 15-epi-lipoxin-a4 by pioglitazone and atorvastatin in the rat

BACKGROUND

Both statins and thiazolidinediones have antiinflammatory properties. However, the exact mechanisms underlying these effects are unknown. We investigated whether atorvastatin (ATV) and pioglitazone (PIO) increase the myocardial content of lipoxin-A4 and 15(R)-epi-lipoxin-A4 (15-epi-LXA4), both arachidonic acid products with strong antiinflammatory properties.

METHODS AND RESULTS

In experiment 1, rats received 3-day pretreatment with water; PIO 2, 5, or 10 mg x kg(-1) x d(-1); ATV 2, 5, or 10 mg x kg(-1) x d(-1); or PIO 10 mg x kg(-1) x d(-1)+ATV 10 mg x kg(-1) x d(-1). In experiment 2, rats received water; PIO 10 mg x kg(-1) x d(-1)+ATV 10 mg x kg(-1) x d(-1); PIO+ATV and valdecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor; PIO+ATV and zileuton, a selective 5-lipoxygenase inhibitor; or zileuton alone. There were 4 rats in each group. Hearts were harvested and analyzed for myocardial lipoxin-A4 and 15-epi-LXA4 levels and for COX-2 and 5-lipoxygenase protein expression. ATV and PIO at 5 and 10 mg x kg(-1) . d(-1) significantly increased myocardial 15-epi-LXA4 levels compared with the sham-treated group (0.51 +/- 0.02 ng/mg). Myocardial 15-epi-LXA4 were significantly higher in the PIO+ATV group (1.29 +/- 0.02 ng/mg; P < 0.001 versus each other group). Both valdecoxib and zileuton abrogated the PIO+ATV increase in 15-epi-LXA4, whereas zileuton alone had no effect. PIO, ATV, and their combination resulted in a small increase in myocardial lipoxin-A4 levels, which was not statistically significant. ATV alone or in combination with PIO markedly augmented COX-2 expression. PIO had a much smaller effect on COX-2 expression. Myocardial expression of 5-lipoxygenase was not altered by PIO, ATV, or their combination.

CONCLUSIONS

Both PIO and ATV increase myocardial levels of 15-epi-LXA4, a mediator with antiinflammatory properties. This finding may explain the antiinflammatory properties of both PIO and ATV.

Insulin sensitizers may prevent metabolic inflammation

The relative decreased response of peripheral tissues to insulin (insulin resistance) is a key metabolic disturbance that predisposes a large percentage of individuals to the development of type 2 diabetes and to cardiovascular disease. As detailed in an extensive literature over the last two decades, insulin resistance co-exists in varying degrees with a variety of other key risk factors, including dyslipidemia, hypertension, and vascular inflammation, that contribute to poor cardiovascular outcomes of individuals with type 2 diabetes and metabolic syndrome. Whereas insulin resistance is generally thought of as pathology unto itself, this commentary suggests that insulin resistance is a physiological compensation to inappropriate oxidative metabolism that induces a metabolic inflammatory response. Via signaling of this inflammatory response, the protective compensation to excessive oxidative metabolism dampens metabolism by reducing insulin action, fatty acid oxidation, and eventually mitochondrial function and numbers. Such a scenario could explain the coexistence of these phenomena with obesity and reduced mitochondrial function. Recent evidence suggests that thiazolidinediones exert pharmacology through modifications of mitochondrial metabolism, preventing the metabolic inflammation and allowing the up regulation of mitochondrial biogenesis. A further understanding of these mechanisms, which are likely to involve key redox signaling events emanating from mitochondrial biochemistry, is needed to fuel new therapeutic advances for the treatment of metabolic syndrome.

Drugs modulating the biological effects of peroxynitrite and related nitrogen species

The term "reactive nitrogen species" includes nitrogen monoxide, commonly called nitric oxide, and some other remarkable chemical entities (peroxynitrite, nitrosoperoxycarbonate, etc.) formed mostly from nitrogen monoxide itself in biological environments. Regardless of the specific mechanisms implicated in their effects, however, it is clear that an integrated pharmacological approach to peroxynitrite and related species is only just beginning to take shape. The array of affected chemical and pathological processes is extremely broad. One of the most conspicuous mechanisms observed thus far has been the scavenging of the peroxynitrite anion by molecules endowed with antioxidant activity. This discovery has in turn lent great significance to several naturally occurring and synthetic antioxidants, which usually protect not only against oxidative reactions, but also from nitrating ones, both in vitro and in vivo. This has proven to be beneficial in different tissues, especially within the central nervous system. Taking these results and those of other biochemical investigations into account, many research lines are currently in progress to establish the true potential of reactive nitrogen species deactivators in the therapy of neurological diseases, ischemia-reperfusion damage, renal failure, and lung injury, among others.

PNU-91325 increases fatty acid synthesis from glucose and mitochondrial long chain fatty acid degradation: a comparative tracer-based metabolomics study with rosiglitazone and pioglitazone in HepG2 cells

The mitochondrial membrane protein termed "mitoNEET," is a putative secondary target for insulin-sensitizing thiazolidinedione (TZD) compounds but its role in regulating metabolic flux is not known. PNU-91325 is a thiazolidinedione derivative which exhibits high binding affinity to mitoNEET and lowers cholesterol, fatty acid and blood glucose levels in animal models. In this study we report the stable isotope-based dynamic metabolic profiles (SIDMAP) of rosiglitazone, pioglitazone and PNU-91325 in a dose-matching, dose-escalating study. One and 10 μM concentrations 1 and 10 μM drug concentrations were introduced into HepG2 cells in the presence of either [1,2-13C2]-D-glucose or [U-13C18]stearate, GC/MS used to determine positional tracer incorporation (mass isotopomer analysis) into multiple metabolites produced by the Krebs and pentose cycles, de novo fatty acid synthesis, long chain fatty acid oxidation, chain shortening and elongation. Rosiglitazone and pioglitazone (10 μM) increased pentose synthesis from [U-13C18]stearate by 127% and 185%, respectively, while PNU-91325 rather increased glutamate synthesis in the Krebs cycle by 113% as compared to control vehicle treated cells. PNU-91325 also increased stearate chain shortening into palmitate by 59%. Glucose tracer-derived de novo palmitate and stearate synthesis were increased by 1 and 10 μM rosiglitazone by 41% and 83%, respectively, and by 63% and 75% by PNU-91325. Stearate uptake was also increased by 10 μM PNU-91325 by 15.8%. We conclude that the entry of acetyl Co-A derived from long-chain fatty acid β-oxidation into the mitochondria is facilitated by the mitoNEET ligand PNU-91325, which increases glucose-derived long chain fatty acid synthesis and breakdown via β-oxidation and anaplerosis in the mitochondria.

Myocardial protection by pioglitazone, atorvastatin, and their combination: mechanisms and possible interactions

We assessed 1) whether pretreatment before ischemia with pioglitazone (Pio) limits infarct size (IS) and whether this protective effect is due to nitric oxide synthase (NOS) and/or prostaglandin production, as has been shown for atorvastatin (ATV); and 2) whether Pio and ATV have synergistic effects on myocardial protection. Sprague-Dawley rats received oral ATV (10 mg.kg-1.day-1), Pio (10 mg.kg-1.day-1), their combination (Pio+ATV), or water alone for 3 days. Additional rats received Pio (10 mg.kg-1.day-1) for 3 days and intravenous SC-58125 [a cyclooxygenase-2 (COX-2) inhibitor] or SC-560 (a COX-1 inhibitor) 15 min before ischemia. Rats underwent 30 min of myocardial ischemia and 4 h of reperfusion, or hearts were harvested for analysis. IS in the Pio and in the ATV groups was significantly smaller than in the sham-treated group. IS in the Pio+ATV group was smaller than in all other groups (P<0.001 vs. each group). The protective effect of Pio was abrogated by SC-58125 but not by SC-560. Pio, ATV, and Pio + ATV increased the expression and activity of cytosolic phospholipase A2 (cPLA2) and COX-2. ATV increased phosphorylated-Akt, phosphorylated-endothelial NOS (P-eNOS), inducible NOS, and COX-2 levels. In contrast, Pio caused an insignificant increase in myocardial levels of phosphorylated-Akt but did not change P-eNOS and iNOS expression. In conclusion, the IS-limiting effects of Pio and ATV involve COX-2. However, the upstream steps differ. ATV induced eNOS phosphorylation and iNOS, cPLA2, and COX-2 expression, whereas Pio induced mainly the expression and activity of cPLA2. The effects of Pio and ATV were additive.

Synthetic peroxisome proliferator-activated receptor-gamma agonists restore impaired vasorelaxation via ATP-sensitive K+ channels by high glucose

The present study was designed to examine whether in the human artery, synthetic peroxisome proliferator-activated receptor (PPAR)-gamma agonists restore vasorelaxation as well as hyperpolarization via ATP-sensitive K+ channels impaired by the high concentration of D-glucose and whether the restoration may be mediated by the antioxidant capacity of these agents. The isometric force and membrane potential of human omental arteries without endothelium were recorded. The production rate of superoxide was evaluated using a superoxide-generating system with xanthine-xanthine oxidase in the absence of smooth muscle cells. Glibenclamide abolished vasorelaxation and hyperpolarization in response to levcromakalim. Addition of D-glucose (20 mM) but not L-glucose (20 mM) reduced this vasorelaxation and hyperpolarization. Synthetic PPAR-gamma agonists (troglitazone and rosiglitazone) and/or an inhibitor of superoxide generation (4,5-dihydroxy-1,3-benzene-disulfonic acid, Tiron), but not a PPAR-alpha agonist (fenofibrate), restored vasorelaxation and hyperpolarization in response to levcromakalim in arteries treated with D-glucose. Troglitazone and rosiglitazone, but not fenofibrate, decreased the production rate of superoxide without affecting uric acid generation. These findings suggest that synthetic PPAR-gamma agonists recover the function of ATP-sensitive K+ channels reduced by the high concentration of glucose in human vascular smooth muscle cells and that the effect of these agonists may be mediated in part by their antioxidant capacity.

Contribution of conjugated linoleic acid to the suppression of inducible nitric oxide synthase expression and transcription factor activation in stimulated mouse mesangial cells

That both infiltrating macrophages and resident mesangial cells express inducible nitric oxide synthase (iNOS) and produce nitric oxide (NO) excessively is crucial to the progress of glomerulonephritis. Although several reports have mentioned the protective impacts of conjugated linoleic acid (CLA) in stimulated macrophages, the role of CLA in glomerular mesangial cells is unknown. The aim of the present study was to explore the ability of CLA to regulate iNOS expression and NO production in stimulated glomerular mesangial cells. Additionally, we evaluated the effect of CLA on activation of transcription factors which mediate iNOS expression. Exogenous CLA dose-dependently diminished iNOS mRNA and protein expression as well as NO production in lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma)-stimulated SV-40-transformed mouse mesangial cells. Electrophoretic mobility shift assay experiments demonstrated that CLA (100 microM) dramatically reduced activation of nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1) and cAMP response element binding protein (CREB) induced by LPS/IFN-gamma. Moreover, addition of 100 microM CLA significantly diminished LPS-IFN-gamma-induced protein degradation of inhibitor kappaB-alpha (IkappaB-alpha) and the protein expression of phosphorylated IkappaB-alpha in the cytosolic fraction as well as nuclear p65 expression (P < 0.05). In summary, inhibition of NF-kappaB, AP-1 and CREB activation by CLA may be associated with the molecular basis for which CLA suppresses iNOS expression and NO production in stimulated mesangial cells.

What has prevented the expansion of insulin sensitisers?

The ability to improve insulin sensitivity with synthetic compounds was uncovered by empirical discoveries by Takeda in the late 1970s. The potential of a class of thiazolidinediones for the treatment of Type 2 diabetes, by decreasing glucose and triglycerides alongside lowering circulating insulin, was made public during the 1980s. As the first of the chemicals (pioglitazone, troglitazone and rosliglitazone) proceeded to clinical trials, these observations were soon extended to demonstrate a rich and complex pharmacology. The promise of this mode of action included prevention of diabetes as well as making a significant impact on the incidence and severity of the life-shortening consequences of the established disease. There are now two of these drugs on the market: pioglitazone and rosiglitazone, and they are being used to treat significant numbers of diabetic patients. However, the use of these drugs and development of future generations of successful candidates has not met the expectations that were held out in the early 1980s. This can be attributed to two major prevailing conditions. Troglitazone became the first thiazolidinedione to be approved as a result of delays in the development of pioglitazone. Unfortunately, troglitazone produced a unique idiosyncratic and sometimes fatal, hepatoxicity that necessitated its removal from the marketplace; second, there has been an incomplete understanding of the biochemical mechanism of action of these drugs that has slowed (and perhaps derailed) attempts to produce second-generation compounds. The latter issue is the subject of this editorial, which suggests that it is time to take a fresh look at the pharmacology of insulin sensitisers.

Receptor-independent actions of PPAR thiazolidinedione agonists: is mitochondrial function the key?

Agonists of the peroxisome proliferator activated receptor gamma (PPAR(gamma)) are currently used for treatment of type 2 diabetes due to their insulin sensitizing and glucose metabolism stabilizing effects. More recently some of these same agonists were shown to exert anti-inflammatory and anti-proliferative effects as well. Although PPAR(gamma) agonists can operate via receptor-mediated events occurring at the genomic level, thereby causing long lasting changes in gene expression patterns, recent studies demonstrate non-genomic as well as genomic actions, and receptor-dependent as well as receptor-independent effects of the thiazolidinedione (TZD) class of PPAR(gamma) agonists. In this review we will summarize data describing some of these novel, receptor independent actions of TZDs, review evidence that TZDs directly influence mitochondrial function, and attempt to reconcile how changes in mitochondrial function could contribute to other receptor-independent actions of these drugs.

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.