Pioglitazone, a PPAR-gamma ligand, provides protection from dextran sulfate sodium-induced colitis in mice in association with inhibition of the NF-kappaB-cytokine cascade

Pioglitazone as a potential modulator in autoimmune diseases: a review on its effects in systemic lupus erythematosus, psoriasis, inflammatory bowel disease, and multiple sclerosis

INTRODUCTION

Current medications for autoimmune disorders often induce broad-ranging side effects, prompting a growing interest in therapies with more specific immune system modulation. Pioglitazone, known for its anti-diabetic properties, is increasingly recognized for significant immunomodulatory potential. Beyond its traditional use in diabetes management, pioglitazone emerges as a promising therapeutic candidate for autoimmune disorders.

AREAS COVERED

This comprehensive review explores pioglitazone's impact on four prominent autoimmune conditions: systemic lupus erythematosus, psoriasis, inflammatory bowel disease, and multiple sclerosis. We focus on pioglitazone's diverse effects on immune cells and cytokines in these diseases, highlighting its potential as a valuable therapeutic option for autoimmune diseases. Here we have reviewed the latest and most current research literature available on PubMed, based on research published in the last 15 years.

EXPERT OPINION

Pioglitazone as an immunomodulatory agent can regulate T cell differentiation, inhibit inflammatory cytokines, and promote anti-inflammatory macrophages. While further clinical studies are needed to fully understand its mechanisms and optimize treatment strategies, pioglitazone represents a potential therapeutic approach to improve outcomes for patients with these challenging autoimmune conditions. The future of autoimmune disease research may involve personalized treatment approaches, and collaborative efforts to improve patient quality of life.

The Complex Relationship Between Microbiota, Immune Response and Creeping Fat in Crohn's Disease

In the last decade, there has been growing interest in the pathological involvement of hypertrophic mesenteric fat attached to the serosa of the inflamed intestinal segments involved in Crohn's disease [CD], known as creeping fat. In spite of its protective nature, creeping fat harbours an aberrant inflammatory activity which, in an already inflamed intestine, may explain why creeping fat is associated with a greater severity of CD. The transmural inflammation of CD facilitates the interaction of mesenteric fat with translocated intestinal microorganisms, contributing to activation of the immune response. This may be not the only way in which microorganisms alter the homeostasis of this fatty tissue: intestinal dysbiosis may also impair xenobiotic metabolism. All these CD-related alterations have a functional impact on nuclear receptors such as the farnesoid X receptor or the peroxisome proliferator-activated receptor γ, which are implicated in regulation of the immune response, adipogenesis and the maintenance of barrier function, as well as on creeping fat production of inflammatory-associated cells such as adipokines. The dysfunction of creeping fat worsens the inflammatory course of CD and may favour intestinal fibrosis and fistulizing complications. However, our current knowledge of the pathophysiology and pathogenic role of creeping fat is controversial and a better understanding might provide new therapeutic targets for CD. Here we aim to review and update the key cellular and molecular alterations involved in this inflammatory process that link the pathological components of CD with the development of creeping fat.

Pioglitazone Attenuates Experimental Colitis-Associated Hyperalgesia through Improving the Intestinal Barrier Dysfunction

Impaired intestinal mucosal integrity during colitis involves the peroxisome proliferator-activated receptor-γ (PPARγ), an important anti-inflammatory factor in intestinal mucosa homoeostasis, which is a potential target in colitis. Recurrent chronic pain is a vital pathogenetic feature of colitis. Nevertheless, potential functions of PPARγ in the colitis-associated hyperalgesia remain unclear. This study aimed to investigate biological roles of pioglitazone in relieving colitis-associated pain hypersensitivity by a PPARγ tight junction protein-dependent mechanism during the course of dextran sodium sulfate (DSS)-induced intestinal inflammation. The DSS-induced colitis model was generated in C57BL/6 mice. Changes in colitis induced the injury of intestinal mucosal barrier and hyperalgesia after a 6-day treatment of pioglitazone (25 mg/kg, IP injection) were assessed through immunofluorescent, hematoxylin and eosin (H&E) staining, western blot analysis, and determination of paw withdrawal mechanical threshold. A significant reduction of paw withdrawal mechanical threshold occurred after DSS treatment. Follow-up data showed that systematic administration of PPARγ agonist pioglitazone ameliorated the DSS-induced colitis and the development of colitis-associated hyperalgesia by repairing the intestinal mucosal barrier. The tight junction proteins ZO-1 and Claudin-5 were upregulated by PPARγ signaling, which in turn promoted the improvement of intestinal barrier function. Moreover, pioglitazone inhibited phosphorylation of ERK and NF-κB in the colon and decreased the levels of inflammatory cytokines in both colon spine tissues. Furthermore, systemically pioglitazone treatment inhibited the activation of microglia and astrocytes, as well as DSS-induced phosphorylation of NR2B subunit in spinal cord, which was correspondingly consistent with the pain behavior. Pioglitazone ameliorates DSS-induced colitis and attenuates colitis-associated mechanical hyperalgesia, with improving integrity of the intestinal mucosal barrier by directly upregulating tight junction proteins. The PPARγ-tight junction protein signaling might be a potential therapeutic target for the treatment of colitis-associated chronic pain.

Pioglitazone-Mediated Attenuation of Experimental Colitis Relies on Cleaving of Annexin A1 Released by Macrophages

Ulcerative colitis and Crohn's disease are chronic inflammatory bowel diseases (IBDs) which burden health systems worldwide; available pharmacological therapies are limited and cost-intensive. Use of peroxisome proliferator activated-receptor γ (PPARγ) ligands for IBD treatment, while promising, lacks solid evidences to ensure its efficacy. Annexin A1 (AnxA1), a glucocorticoid-modulated anti-inflammatory protein, plays a key role on IBD control and is a potential biomarker of IBD progression. We here investigated whether effects of pioglitazone, a PPARγ ligand, rely on AnxA1 actions to modulate IBD inflammation. Experimental colitis was evoked by 2% dextran sodium sulfate (DSS) in AnxA1 knockout (AnxA1^-/-) or wild type (WT) C57BL/6 mice. Clinical and histological parameters were more severe for AnxA^-/- than WT mice, and 10 mg/kg pioglitazone treatment attenuated disease parameters in WT mice only. AnxA1 expression was increased in tissue sections of diseased WT mice, correlating positively with presence of CD68⁺ macrophages. Metalloproteinase-9 (MMP-9) and inactive 33 kDa AnxA1 levels were increased in the colon of diseased WT mice, which were reduced by pioglitazone treatment. Cytokine secretion, reactive oxygen species generation and MMP-9 expression caused by lipopolysaccharide (LPS) treatment in AnxA1-expressing RAW 264.7 macrophages were reduced by pioglitazone treatment, effects not detected in AnxA1 knockdown macrophages. LPS-mediated increase of AnxA1 cleaving in RAW 264.7 macrophages was also attenuated by pioglitazone treatment. Finally, pioglitazone treatment increased extracellular signal-regulated kinase (ERK) phosphorylation in AnxA1-expressing RAW 264.7 macrophages, but not in AnxA1-knockdown macrophages. Thus, our data highlight AnxA1 as a crucial factor for the therapeutic actions of pioglitazone on IBDs.

Interventions of natural and synthetic agents in inflammatory bowel disease, modulation of nitric oxide pathways

Inflammatory bowel disease (IBD) refers to a group of disorders characterized by chronic inflammation of the gastrointestinal (GI) tract. The elevated levels of nitric oxide (NO) in serum and affected tissues; mainly synthesized by the inducible nitric oxide synthase (iNOS) enzyme; can exacerbate GI inflammation and is one of the major biomarkers of GI inflammation. Various natural and synthetic agents are able to ameliorate GI inflammation and decrease iNOS expression to the extent comparable with some IBD drugs. Thereby, the purpose of this study was to gather a list of natural or synthetic mediators capable of modulating IBD through the NO pathway. Electronic databases including Google Scholar and PubMed were searched from 1980 to May 2018. We found that polyphenols and particularly flavonoids are able to markedly attenuate NO production and iNOS expression through the nuclear factor κB (NF-κB) and JAK/STAT signaling pathways. Prebiotics and probiotics can also alter the GI microbiota and reduce NO expression in IBD models through a broad array of mechanisms. A number of synthetic molecules have been found to suppress NO expression either dependent on the NF-κB signaling pathway (i.e., dexamethasone, pioglitazone, tropisetron) or independent from this pathway (i.e., nicotine, prednisolone, celecoxib, β-adrenoceptor antagonists). Co-administration of natural and synthetic agents can affect the tissue level of NO and may improve IBD symptoms mainly by modulating the Toll like receptor-4 and NF-κB signaling pathways.

Peroxisome Proliferator-Activated Receptors: Experimental Targeting for the Treatment of Inflammatory Bowel Diseases

The peroxisome proliferator-activated receptors (PPARs) are a group of nuclear receptor proteins that promote ligand-dependent transcription of target genes that regulate energy production, lipid metabolism, and inflammation. The PPAR superfamily comprises three subtypes, PPARα, PPARγ, and PPARβ/δ, with differential tissue distributions. In addition to their different roles in the regulation of energy balance and carbohydrate and lipid metabolism, an emerging function of PPARs includes normal homeostasis of intestinal tissue. PPARα activation represses NF-κB signaling, which decreases the inflammatory cytokine production by different cell types, while PPARγ ligands can inhibit activation of macrophages and the production of inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and Il-1β. In this regard, the anti-inflammatory responses induced by PPAR activation might restore physiopathological imbalances associated with inflammatory bowel diseases (IBD). Thus, PPARs and their ligands have important therapeutic potential. This review briefly discusses the roles of PPARs in the physiopathology and therapies of the most important IBDs, ulcerative colitis (UC), and Crohn's disease (CD), as well some new experimental compounds with PPAR activity as promising drugs for IBD treatment.

Combined Rosiglitazone and Forskolin Have Neuroprotective Effects in SD Rats after Spinal Cord Injury

The peroxisome proliferator-activated receptor gamma (PPAR-γ) agonist rosiglitazone inhibits NF-κB expression and endogenous neural stem cell differentiation into neurons and reduces the inflammatory cascade after spinal cord injury (SCI). The aim of this study was to explore the mechanisms underlying rosiglitazone-mediated neuroprotective effects and regulation of the balance between the inflammatory cascade and generation of endogenous spinal cord neurons by using a spinal cord-derived neural stem cell culture system as well as SD rat SCI model. Activation of PPAR-γ could promote neural stem cell proliferation and inhibit PKA expression and neuronal formation in vitro. In the SD rat SCI model, the rosiglitazone + forskolin group showed better locomotor recovery compared to the rosiglitazone and forskolin groups. MAP2 expression was higher in the rosiglitazone + forskolin group than in the rosiglitazone group, NF-κB expression was lower in the rosiglitazone + forskolin group than in the forskolin group, and NeuN expression was higher in the rosiglitazone + forskolin group than in the forskolin group. PPAR-γ activation likely inhibits NF-κB, thereby reducing the inflammatory cascade, and PKA activation likely promotes neuronal cell regeneration.

Anti-Inflammatory Effects of Schisandrin B on LPS-Stimulated BV2 Microglia via Activating PPAR-γ

Schisandrin B (Sch B), a dibenzocyclooctadiene lignan isolated from Schisandra chinensis (Turcz.) Baill, has been shown to have anti-inflammatory effect. The purpose of this study was to evaluate the effect of Sch B on LPS-induced inflammation in microglia and to investigate the molecular targets of Sch B. BV2 cells were stimulated by LPS in the presence or absence of Sch B. The results showed that the levels of TNF-α, IL-6, IL-1β, and PGE₂ upregulated by LPS were significantly suppressed by Sch B. LPS-induced NF-κB activation was also inhibited by Sch B. Furthermore, Sch B was found to upregulate the expression of PPAR-γ in a concentration-dependent manner. In addition, the inhibition of Sch B on TNF-α, IL-6, IL-1β, and PGE₂ production were reversed by PPAR-γ antagonist GW9662. In conclusion, these results suggested that Sch B inhibited LPS-induced inflammatory response by activating PPAR-γ.

Adipokines and the role of visceral adipose tissue in inflammatory bowel disease

Recently, adipocytes have been recognized as actively participating in local and systemic immune responses via the secretion of peptides detectable in relevant levels in the systemic circulation, the so-called "adipo(cyto)kines". Multiple studies appearing within the last 10-15 years have focused on the possible impact of adipose tissue depots on inflammatory bowel disease (IBD). Consequently, various hypotheses regarding the role of different adipokines in inflammatory diseases in general and in intestinal inflammatory processes in particular have been developed and have been further refined in recent years. After a focused summary of the data reported concerning the impact of visceral adipose tissue on IBD, such as Crohn's disease and ulcerative colitis, our review focuses on recent developments indicating that adipocytes as part of the innate immune system actively participate in antimicrobial host defenses in the context of intestinal bacterial translocation, which are of utmost importance for the homeostasis of the whole organism. Modulators of adipose tissue function and regulators of adipokine secretion, as well as modifiers of adipocytic pattern recognition molecules, might represent future potential drug targets in IBD.

Protective effect of simvastatin and rosuvastatin on trinitrobenzene sulfonic acid-induced colitis in rats

Objective:

Statins have anti-inflammatory effects that are not directly related to their cholesterol lowering activity. This study was carried out to evaluate the effect of simvastatin or rosuvastatin on the extent of colonic mucosal damage and on the inflammatory response in trinitrobenzene sulfonic acid (TNBS)-induced ulcerative colitis.

Materials and Methods:

Ulcerative colitis was induced by single intrarectal injection of 120 mg/kg TNBS. Test groups were treated with simvastatin (10 mg/kg, p.o.) or rosuvastatin (10 mg/kg, p.o.). Colonic mucosal inflammation was evaluated clinically, biochemically, and histologically.

Result:

Disease activity index score in TNBS-treated rats, as determined by weight loss, stool consistency, fecal occult blood, were significantly lowers in simvastatin or rosuvastatin-treated rats than TNBS-treated animals. Simvastatin or rosuvastatin counteracted the reduction in colon length, decreased colon weight, neutrophil accumulation, and tumor necrosis factor-alpha level in TNBS-induced colitis. Simvastatin and rosuvastatin also inhibited the increase in oxidative stress levels after TNBS administration.

Conclusions:

These results suggest that simvastatin and rosuvastatin significantly ameliorate experimental colitis in rats, and these effects could be explained by their anti-inflammatory and antioxidant activity.

TLR4 at the Crossroads of Nutrients, Gut Microbiota, and Metabolic Inflammation

Obesity is accompanied by the activation of low-grade inflammatory activity in metabolically relevant tissues. Studies have shown that obesity-associated insulin resistance results from the inflammatory targeting and inhibition of key proteins of the insulin-signaling pathway. At least three apparently distinct mechanisms-endoplasmic reticulum stress, toll-like receptor (TLR) 4 activation, and changes in gut microbiota-have been identified as triggers of obesity-associated metabolic inflammation; thus, they are expected to represent potential targets for the treatment of obesity and its comorbidities. Here, we review the data that place TLR4 in the center of the events that connect the consumption of dietary fats with metabolic inflammation and insulin resistance. Changes in the gut microbiota can lead to reduced integrity of the intestinal barrier, leading to increased leakage of lipopolysaccharides and fatty acids, which can act upon TLR4 to activate systemic inflammation. Fatty acids can also trigger endoplasmic reticulum stress, which can be further stimulated by cross talk with active TLR4. Thus, the current data support a connection among the three main triggers of metabolic inflammation, and TLR4 emerges as a link among all of these mechanisms.

PPARγ in Inflammatory Bowel Disease

Peroxisome proliferator-activated receptor gamma (PPARγ) is member of a family of nuclear receptors that interacts with nuclear proteins acting as coactivators and corepressors. The colon is a major tissue which expresses PPARγ in epithelial cells and, to a lesser degree, in macrophages and lymphocytes and plays a role in the regulation of intestinal inflammation. Indeed, both natural and synthetic PPARγ ligands have beneficial effects in different models of experimental colitis, with possible implication in the therapy of inflammatory bowel disease (IBD). This paper will specifically focus on potential role of PPARγ in the predisposition and physiopathology of IBD and will analyze its possible role in medical therapy.

PPAR gamma, bioactive lipids, and cancer progression

In this article we review the evolution of cancer research involving PPARgamma, including mechanisms, target genes, and clinical applications. For the last thirteen years, the effects of PPARgamma activity on tumor biology have been studied intensely. Most of this research has focused upon the potential for employing agonists of this nuclear receptor in cancer treatment. As a monotherapy such agonists have shown little success in clinical trials, while they have shown promise as components of combination treatments both in culture and in animal models. Other investigations have explored a possible role for PPARgamma as a tumor suppressor, and as an inducer of differentiation of cancer stem cells. Whereas early studies have yielded variable conclusions regarding the prevalence of PPARgamma mutations in cancer, the protein level of this receptor has been more recently identified as a significant prognostic marker. We predict that indicators of PPARgamma activity may also serve as predictive markers for tailoring treatments.

Carbon monoxide liberated from carbon monoxide-releasing molecule exerts an anti-inflammatory effect on dextran sulfate sodium-induced colitis in mice

BACKGROUND

Endogenous carbon monoxide (CO) is one of the three products of heme degradation by heme oxygenase-1 (HO-1) and exerts novel anti-inflammatory and anti-apoptotic effects as a gaseous second messenger. The purpose of this investigation was to determine whether exogenous CO could modulate intestinal inflammation.

METHODS

Acute colitis was induced with 2% DSS in male C57BL/6 mice. CO-releasing molecule-2 (CORM-2; tricarbonyldichlororuthenium(II) dimer) was intraperitoneally administered twice daily and the disease activity index (DAI) was determined. We measured tissue-associated myeloperoxidase (MPO) activity as an index of neutrophil infiltration, and the production of keratinocyte chemoattractant (KC) and tumor necrosis factor-α (TNF-α) protein in the intestinal mucosa. In an in-vitro study, young adult mouse colonic epithelial (YAMC) cells were incubated with TNF-α, and KC mRNA/protein expression and nuclear translocation of nuclear factor-kappa B (NF-κB) were measured with or without CORM-2 treatment.

RESULTS

After DSS administration, DAI score increased in a time-dependent manner, and this increase was ameliorated by CORM-2 treatment. Increases in MPO activity and in the production of KC and TNF-α after DSS administration were significantly inhibited by CORM-2. TNF-α-induced KC production in YAMC cells was also inhibited by CORM-2 treatment. Further, nuclear translocation of NF-κB in YAMC cells was inhibited by CORM-2.

CONCLUSION

CORM-liberated CO significantly inhibited inflammatory response in murine colitis by inhibition of cytokine production in the colonic epithelium. These results suggest that CO could become a new therapeutic molecule for inflammatory bowel disease.

β-Caryophyllene inhibits dextran sulfate sodium-induced colitis in mice through CB2 receptor activation and PPARγ pathway

Cannabinoid receptor 2 (CB2) activation is suggested to trigger the peroxisome proliferator-activated receptor-γ (PPARγ) pathway, and agonists of both receptors improve colitis. Recently, the plant metabolite (E)-β-caryophyllene (BCP) was shown to bind to and activate CB2. In this study, we examined the anti-inflammatory effect of BCP in dextran sulfate sodium (DSS)-induced colitis and analyzed whether this effect was mediated by CB2 and PPARγ. Oral treatment with BCP reduced disease activity, colonic macro- and microscopic damage, myeloperoxidase and N-acetylglucosaminidase activities, and levels and mRNA expression of colonic tumor necrosis factor-α, IL-1β, interferon-γ, and keratinocyte-derived chemokine. BCP treatment also inhibited the activation of extracellular signal-regulated kinase 1/2, nuclear factor κB, IκB-kinase α/β, cAMP response element binding and the expression of caspase-3 and Ki-67. Moreover, BCP enhanced IL-4 levels and forkhead box P3 mRNA expression in the mouse colon and reduced cytokine levels (tumor necrosis factor-α, keratinocyte-derived chemokine, and macrophage-inflammatory protein-2) in a culture of macrophages stimulated with lipopolysaccharide. The use of the CB2 antagonist AM630 or the PPARγ antagonist GW9662 significantly reversed the protective effect of BCP. Confirming our results, AM630 reversed the beneficial effect of BCP on pro-inflammatory cytokine expression in IEC-6 cells. These results demonstrate that the anti-inflammatory effect of BCP involves CB2 and the PPARγ pathway and suggest BCP as a possible therapy for the treatment of inflammatory bowel disease.

Ulcerative colitis: immune function, tissue fibrosis and current therapeutic considerations

BACKGROUND

Ulcerative colitis (UC) is a complex disease in which the interaction of genetic, environmental and microbial factors drives chronic intestinal inflammation that finally leads to extensive tissue fibrosis.

DISCUSSION

The present review discusses the current knowledge on genetic susceptibility, especially of the IL-12/IL-23 pathway, the pathophysiologic role of the involved cytokines (e.g. IL-13, IL-23, TGFβ1) and immune cells (e.g. T cells, epithelial cells, fibroblasts) in UC followed by an overview on actual therapeutic considerations. These future therapies will target selectively the involved cell types by blocking their activation and its downstream signalling, by inhibiting their migration to the inflamed site and by anti-cytokine strategies. This may avoid-when initiated in time-the perpetuation of the inflammatory mechanisms thus preventing fibrosis. With respect to animal models that have guided the most productive efforts for understanding human inflammatory bowel disease, these will be shortly discussed in the respective context.

Ulcerative colitis: immune function, tissue fibrosis and current therapeutic considerations

BACKGROUND

Ulcerative colitis (UC) is a complex disease in which the interaction of genetic, environmental and microbial factors drives chronic intestinal inflammation that finally leads to extensive tissue fibrosis.

DISCUSSION

The present review discusses the current knowledge on genetic susceptibility, especially of the IL-12/IL-23 pathway, the pathophysiologic role of the involved cytokines (e.g. IL-13, IL-23, TGFβ1) and immune cells (e.g. T cells, epithelial cells, fibroblasts) in UC followed by an overview on actual therapeutic considerations. These future therapies will target selectively the involved cell types by blocking their activation and its downstream signalling, by inhibiting their migration to the inflamed site and by anti-cytokine strategies. This may avoid-when initiated in time-the perpetuation of the inflammatory mechanisms thus preventing fibrosis. With respect to animal models that have guided the most productive efforts for understanding human inflammatory bowel disease, these will be shortly discussed in the respective context.

Inhibitory effect of rosiglitazone on the acid-induced intracellular generation of hydrogen peroxide in cultured feline esophageal epithelial cells

Peroxisome proliferator-activated receptor-gamma (PPARγ) agonists have been reported to enhance antioxidant defenses by increasing levels of catalase and copper-zinc superoxide dismutase (Cu/Zn SOD) in oligodendrocyte progenitor cells. In this study, we investigated the effects of the PPARγ agonist, rosiglitazone, on hydrogen peroxide (H(2)O(2)) generation by acidified medium at pH 5.5 (AM5.5), which is in the pH range of duodenogastric refluxates, in primary cultured feline esophageal epithelial cells (EEC). Successful isolation of EEC was identified by immunocytochemistry. AM5.5- and rosiglitazone-induced cell viabilities were determined using 3-(4,5-dimethylthiozol-2-yl)-2,5-diphenyltetrazolium bromide assays. The NAD(P)H oxidase activity was measured, and expression of catalase or SOD protein by AM5.5 in the absence and presence of rosiglitazone was assessed using western blotting analysis. PPARγ protein and mRNA were constitutively expressed in EEC. In the incubation with rosiglitazone alone, cell viability was shown more than 90% at 0-10 μM for 72 h. After exposure to AM5.5 for 8 h, intracellular H(2)O(2) was significantly generated. Treatment with rosiglitazone prior to and during exposure to AM5.5 inhibited the H(2)O(2) generation whereas the specific PPARγ antagonist GW9662 offsets the inhibitory action of rosiglitazone. H(2)O(2) generation was also prevented by a nonspecific ROS scavenger N-acetylcysteine or an inhibitor of NADPH oxidase diphenyleneiodonium. The enhanced AM5.5-induced NAD(P)H oxidase activity was not suppressed by rosiglitazone. Instead, the pretreatment of rosiglitazone enhanced the protein expression of catalase, Cu/Zn SOD, and Mn SOD, which are endogenous antioxidative enzymes. These findings indicate that rosiglitazone inhibits AM5.5-induced intracellular H(2)O(2) production, which occurs via NAD(P)H oxidase activation, by using a PPARγ-dependent pathway, and that the underlying mechanism involves an increase in the expression of catalase and SOD proteins.

Gastrointestinal Cytoprotection by PPARγ Ligands

Peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor that is known to play a central role in lipid metabolism and insulin sensitivity as well as inflammation and cell proliferation. According to the results obtained from studies on several animal models of gastrointestinal inflammation, PPARγ has been implicated in the regulation of the immune response, particularly inflammation control, and has gained importance as a potential therapeutic target in the management of gastrointestinal inflammation. In the present paper, we present the current knowledge on the role of PPARγ ligands in the gastrointestinal tract.

Identification of inflammation-related proteins in a murine colitis model by 2D fluorescence difference gel electrophoresis and mass spectrometry

BACKGROUND AND AIMS

The aim of this study was to identify new intestinal proteins potentially associated with acute inflammation using proteomic profiling of an in vivo mice model of ulcerative colitis.

METHODS

2D fluorescence difference gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption/ionization time-of-flight spectrometer (MALDI-TOF) peptide mass fingerprinting were used to determine differentially expressed proteins between normal and inflamed intestinal mucosa. Acute colitis was induced by 8.0% dextran sodium sulfate (DSS) given p.o. for 7 days.

RESULTS

Among a total of seven protein spots showing differential expression, we identified five different proteins, of which two were upregulated and three downregulated in colitis in comparison to normal mucosa, using the MASCOT search engine. 3-Hydroxy-3-methylglutaryl-coenzyme A synthase 2 and serpin b1a were upregulated proteins, and protein disulfide-isomerase A3, peroxiredoxin-6 and vimentin were identified as downregulated proteins.

CONCLUSION

These identified proteins may be responsible for the development of the intestinal inflammation. 2D-DIGE and MALDI-TOF mass spectrometry are useful in the search for the differentially expressed proteins.

Food-derived bioactives as potential regulators of the IL-12/IL-23 pathway implicated in inflammatory bowel diseases

The gene-specific modulation of inflammatory cytokines by food bioactives represents a possible approach to the nutritional or pharmaceutical prevention and treatment of inflammatory bowel disease (IBD). There is evidence for a key role of the interleukin-12beta1/23 receptor (IL-12 Rbeta1/23 R) pathway in IBD, and that reduction of the normal expression of the IL-23 R gene may provide a therapeutic target for this disease. The binding of interleukin-23 (IL-23) to its receptor IL-23 R regulates a newly defined effector T-cell subset, Th17 cells, characterised by the production of interleukin-17 (IL-17) and other cytokines, including tumour necrosis factor-alpha (TNF-alpha). In this study we developed an assay that measured IL-17 and TNF-alpha expression after incubation with specific dietary bioactives in the human T-cell Kit 225. It is anticipated that these changes will reflect differences in IL-23 R production, albeit indirectly. The cell line Kit 225 has similarities to Th17 cells, a subset of T cells producing IL-17 and TNF-alpha, and in initial experiments we demonstrated that the cells express both IL-23 receptor subunits, as well as IL-17 and TNF-alpha genes. Upon verification that stimulation of Kit 225 cells with 1ng/mL IL-23 significantly upregulated IL-17 and TNF-alpha gene expression, and IL-17 production, we supplemented cells with selected food bioactives, caffeic acid phenethyl ester (CAPE), epigallocatechin gallate (EGCG), docosahexaenoic acid (DHA), and linoleic acid (LA), and with phorbol myristate acetate (PMA) and sodium salicylate, used as pro-inflammatory and anti-inflammatory controls, respectively. In both unstimulated cells and after IL-23 stimulation, bioactives modulated the pro-inflammatory cytokines involved in IBD, underlining the possible role of foods in this disease. EGCG and DHA, which significantly inhibited both IL-17 and TNF-alpha expression, appeared particularly interesting.

The many faces of PPARgamma: anti-inflammatory by any means?

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily, a group of transcription factors that regulate expression of their target genes upon ligand binding. As endogenous ligands, oxidized fatty acids and prostanoids can bind to and activate the receptor. Natural and synthetic PPARgamma activators have been studied extensively in many inflammatory settings and in most instances they have been shown to be anti-inflammatory. In this review we give an overview of the different molecular mechanisms how PPARgamma and its agonists exert their anti-inflammatory effects both at the cellular level and the level of the organism. The action of PPARgamma in acute and chronic inflammatory diseases and disease models will be presented.

Comparison of cytokine modulation by natural peroxisome proliferator-activated receptor gamma ligands with synthetic ligands in intestinal-like Caco-2 cells and human dendritic cells--potential for dietary modulation of peroxisome proliferator-activated receptor gamma in intestinal inflammation

BACKGROUND

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays a role in the regulation of intestinal inflammation and is activated by both natural (polyunsaturated fatty acid; PUFAs) and synthetic (troglitazone) ligands. The fatty acid content of defined formula diets may play a role in mediating the antiinflammatory effect, but the mechanism is unclear.

OBJECTIVE

We evaluated to what extent the effect of PUFAs on intestinal inflammation is mediated via PPARgamma.

DESIGN

The human enterocyte-like cell line Caco-2 and human dendritic cells were stimulated by interleukin (IL) 1beta and lipoprotein polysaccharide, respectively, in the presence of PPARgamma agonists (troglitazone or PUFAs) or antagonist (GW9662). Five PUFAs were tested: alpha-linolenic acid (ALA), conjugated linoleic acid (CLA), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and gamma-linolenic acid (GLA). Cytokine production was measured by enzyme-linked immunosorbent assay and PPARgamma, I-kappaB, and inducible nitric oxide synthase (iNOS) expression by Western blot.

RESULTS

In Caco-2 cells, IL-6 secretion was significantly decreased by troglitazone, DHA, EPA, and GLA. IL-8 production was significantly decreased by troglitazone, ALA, DHA, EPA, and GLA. PPARgamma expression was significantly increased by troglitazone, DHA, and EPA. iNOS expression was significantly decreased by troglitazone, DHA, and EPA. Troglitazone and PUFAs at 0.1 mumol/L tended to increase the expression of I-kappaB. Addition of GW9662 reversed the effect of troglitazone and PUFAs at 0.1 mumol/L on IL-8 production and decreased the expression of PPARgamma. EPA and DHA also modulated the dendritic cell response to lipoprotein polysaccharide.

CONCLUSIONS

The tested PUFAs exerted an antiinflammatory effect in vitro in both models. This effect of PUFAs in Caco-2 cells is similar to that of troglitazone on intestinal inflammation mediated by PPARgamma, and the potency of the antiinflammatory effect is linked to the number of double bonds.

A Role for the PPARgamma in Cancer Therapy

In 1997, the first published reports highlighted PPARgamma as a novel cancer therapeutic target regulating differentiation of cancer cells. A subsequent flurry of papers described these activities more widely and fuelled further enthusiasm for differentiation therapy, as the ligands for the PPARgamma were seen as well tolerated and in several cases well-established in other therapeutic contexts. This initial enthusiasm and promise was somewhat tempered by contradictory findings in several murine cancer models and equivocal trial findings. As more understanding has emerged in recent years, a renaissance has occurred in targeting PPARgamma within the context of either chemoprevention or chemotherapy. This clarity has arisen in part through a clearer understanding of PPARgamma biology, how the receptor interacts with other proteins and signaling events, and the mechanisms that modulate its transcriptional actions. Equally greater translational understanding of this target has arisen from a clearer understanding of in vivo murine cancer models. Clinical exploitation will most likely require precise and quantifiable description of PPARgamma actions, and resolution of which targets are the most beneficial to target combined with an understanding of the mechanisms that limits its anticancer effectiveness.

Interleukin-10 is upregulated by nanomolar rosiglitazone treatment of mature dendritic cells and human CD4+ T cells

Activators of peroxisome proliferator-activated receptor (PPAR)-gamma are anti-inflammatory and have been proposed as therapeutic agents for the treatment of Th1-type inflammatory diseases. We report that nanomolar concentrations of rosiglitazone enhance the production of IL-10 from activated human mature monocyte-derived dendritic cells. Also, rosiglitazone specifically induces the production of IL-10 from TCR-activated human CD4+ T cells and that this effect is PPAR-gamma-dependent. We also demonstrate for the first time the presence of a functional PPAR response element (PPRE) in the human IL-10 promoter region. Finally we show that rosiglitazone can induce IL-10 in combination with 1,25 alpha-dihydroxyvitamin D3 to a greater extent than each treatment alone. In summary our findings demonstrate that IL-10 is upregulated by nanomolar TZDs in immune cells, and this may, in part, be responsible for the potential anti-inflammatory effects of PPAR-gamma in humans.

Rosiglitazone Suppresses Cyclosporin-Induced Chronic Transplant Dysfunction and Prolongs Survival of Rat Cardiac Allografts

BACKGROUND

The lack of effective treatment for chronic transplant dysfunction restricts the long-term survival of solid organ allografts. Peroxisome proliferator-activated receptor ligands can suppress vascular inflammation. The aim of this study was to analyze the effects of rosiglitazone on chronic transplant dysfunction in a rat cardiac transplant model.

METHODS

Inbred male Fisher 344 (F344, RT1lvl) and Lewis (LEW, RT1(1)) rats were subjected to heterotopic abdominal heart transplantation according to standard procedures. Cyclosporine A was administered intraperitoneally to cover acute rejection, and rosiglitazone was administered orally by gavage daily from 3 days before the operation to the end of experiments.

RESULTS

Rosiglitazone significantly prolonged the survival of cardiac allografts in rats (F344 to LEW) that had received a 10-day course of cyclosporin A compared to treatment with immunosuppressant alone. Analysis of allografts at 120 days posttransplantation showed that rosiglitazone reduced the inflammatory cell infiltrate in both the vessels and graft parenchyma as were neointimal formation, vascular occlusion, and fibrosis. Expression of transforming growth factor-beta and related proteins was less abundant after cyclosporin A/rosiglitazone treatment.

CONCLUSIONS

The findings reported here demonstrate that rosiglitazone given under the cover of short-term treatment with cyclosporin A prolongs cardiac allograft survival and reduces the severity of chronic transplant dysfunction. This may be mediated in part through the downregulation of transforming growth factor-beta and related proteins. The combined effects of rosiglitazone and immunosuppressive drugs are potentially beneficial to patients receiving organ transplants.

13-Oxo-ODE is an endogenous ligand for PPARgamma in human colonic epithelial cells

BACKGROUND

The ligand activated nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPARgamma) induces transcriptional repression of pro-inflammatory factors. Activation of PPARgamma is followed by amelioration of colitis in animal models of inflammatory bowel disease (IBD). A reduced expression of PPARgamma was found in epithelial cells of patients with ulcerative colitis. The eicosanoids 13-HODE and 15-HETE are products of 12/15-lipoxygenase (LOX) and endogenous ligands for PPARgamma. Dehydrogenation of 13-HODE by 13-HODE dehydrogenase results in formation of the 13-Oxo-ODE. Highest activity of 13-HODE dehydrogenase is found in colonic epithelial cells (CECs). We therefore investigated whether 13-Oxo-ODE is a new endogenous ligand of PPARgamma in CECs.

METHODS

LOX activity and 13-HODE dehydrogenase in CECs were investigated after stimulation with arachidonic or linoleic acid. LOX metabolites were identified by RP-18 reversed-phase HPLC. Binding of (14)C-labelled 13-Oxo-ODE was demonstrated using a His-tagged PPARgamma.

RESULTS

Stimulation of HT-29 and primary CECs homogenates with and without Ca-ionophor was followed by the formation of high amounts of the linoleic acid metabolite 13-Oxo-ODE (155 and 85 ng/ml). The decrease of IL-8 secretion from IEC was more pronounced after pre-incubation with 13-Oxo-ODE compared to the PPARgamma agonist troglitazone and higher as with the known PPARgamma ligands 13-HODE and 15-HETE. Binding assays with (14)C-labelled 13-Oxo-ODE clearly demonstrated a direct interaction.

CONCLUSION

High amounts of 13-Oxo-ODE can be induced in CECs by stimulation of linoleic acid metabolism. 13-Oxo-ODE binds to PPARgamma and has anti-inflammatory effects. 13-HODE dehydrogenase might be a therapeutic target in IBD.

The role of PPARgamma on restoration of colonic homeostasis after experimental stress-induced inflammation and dysfunction

BACKGROUND & AIMS

Psychological stress has been implicated in the clinical course of several gastrointestinal diseases, but the mechanisms implicated and the effects of stress on the normal colon are not yet fully understood.

METHODS

Male Wistar rats were exposed to various immobilization periods as a stress paradigm. Colon was processed to assess myeloperoxidase activity, nitric oxide synthase 2, cyclooxygenase 2, and peroxisome proliferator-activated receptor gamma (PPARgamma) expression and production of prostaglandins. Colonic permeability, bacterial translocation, tight junctions ultrastructure, and immunoglobulin (Ig) A levels were also evaluated.

RESULTS

Exposure to acute (6 hours) immobilization stress produced an increase in myeloperoxidase activity and nitric oxide synthase 2 and cyclooxygenase 2 expression. All these parameters remained increased after 5 days of repeated stress exposure, showing a trend to normalize after 10 days. Levels of the anti-inflammatory eicosanoid 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) and expression of PPARgamma run parallel with these changes. Colonic epithelial barrier was altered after stress exposure, and a significant decrease in colonic IgA levels after acute stress exposure was observed. Pretreatment with PPARgamma agonists 15d-PGJ(2) and rosiglitazone prevented colonic inflammation and barrier dysfunction as well as the decrease of IgA production induced after acute stress; PPARgamma specific antagonist T0070907 reverted these effects.

CONCLUSIONS

Activation of PPARgamma in rat colon in vivo seems to counteract colonic inflammation and dysfunction induced by stress. On the other hand, PPARgamma ligands may be therapeutically useful in conditions in which inflammation and barrier dysfunction takes place in colon after exposure to stress.

Pioglitazone inhibits connective tissue growth factor expression in advanced atherosclerotic plaques in low-density lipoprotein receptor-deficient mice

Connective tissue growth factor (CTGF) is expressed in atherosclerotic plaques. It is generally recognized that CTGF contributes to atherosclerosis by stimulating vascular smooth muscle cell (VSMC) proliferation and extracellular matrix production during the development of atherosclerosis. Recent studies indicate that CTGF may also contribute to plaque destabilization as it induces apoptosis and stimulates MMP-2 expression in VSMCs. Thiazolidinediones (TZDs), a new class of insulin sensitizing drugs for type 2 diabetes, inhibit atherosclerosis. However, their effect on CTGF expression in atherosclerotic plaques remains unknown. In this study, male LDL receptor-deficient mice were fed high-fat diet for 4 months to induce the formation of atherosclerotic plaques and then given the high-fat diet with or without pioglitazone for the next 3 months. At the end of the 7-month study, CTGF expression in aortic atherosclerotic lesions was examined. Results showed that CTGF expression was increased in mice fed the high-fat diet by seven-fold as compared to that in mice fed normal chow, but the treatment with pioglitazone significantly inhibited the high-fat diet-induced CTGF expression. To verify these in vivo observations, in vitro studies using human aortic SMC were conducted. Quantitative real-time PCR and Western blot showed that pioglitazone inhibited TGF-beta-stimulated CTGF expression. In conclusion, the present study has demonstrated that pioglitazone inhibits CTGF expression in mouse advanced atherosclerotic plaques and in cultured human SMCs, and hence unveiled a possible mechanism potentially involved in the inhibition of atherosclerosis by TZD.

Administration of pioglitazone in low-density lipoprotein receptor-deficient mice inhibits lesion progression and matrix metalloproteinase expression in advanced atherosclerotic plaques

Recent clinical trials have provided evidence that pioglitazone reduces cardiovascular events in patients with type 2 diabetes. However, the underlying mechanisms are not well understood. Because it has been well established that disruption of atherosclerotic plaques is a key event involved in acute myocardial infarction, we hypothesized that pioglitazone reduces cardiovascular events by stabilizing atherosclerotic lesions. In this study, we used an animal model to test our hypothesis. Low-density lipoprotein receptor-deficient (LDLR-/-) male mice were first fed a high-fat diet for 4 months to induce the formation of aortic atherosclerotic plaques and then treated with pioglitazone for the next 3 months. Analysis of atherosclerotic plaques at the end of the study showed that treatment with pioglitazone at 20 mg/kg/day reduced the progression of atherosclerotic plaques as compared to untreated mice. Furthermore, gene array analysis, quantitative real-time polymerase chain reaction, and immunohistochemical analysis showed that pioglitazone inhibited high-fat diet-induced upregulation of matrix metalloproteinase (MMP) expression. Finally, Sirius red staining showed that atherosclerotic lesions in mice receiving pioglitazone had higher collagen contents than those in untreated mice. This study demonstrated for the first time that administration of pioglitazone in LDLR-/- mice inhibited lesion progression and MMP expression in established atherosclerotic plaques and thus delineated a potential mechanism by which pioglitazone reduces cardiovascular events in patients with type 2 diabetes.

The PPARgamma agonist rosiglitazone impairs colonic inflammation in mice with experimental colitis

Various animal models showed that peroxisome proliferator-activated receptor (PPAR)γ agonists, when given as a gavage shortly preceding colitis induction, protect against inflammatory bowel disease (IBD). We have examined the effects of 16 days rosiglitazone treatment via the diet prior to dextran sodium sulphate (DSS)-induced colitis in mice. After 7 days DSS in the drinking water, rosiglitazone-fed mice had lost significantly more weight than control mice. Rosiglitazone-treated mice had more diarrhea, weight of colon and spleen were increased, and length of colon was decreased. Histology showed that rosiglitazone-treated mice had more severe colitis, mainly caused by more ulceration, crypt loss, and edema. Immunofluorescence showed a loss of tight junction structure Zonula Occludens protein 1 (ZO-1) in colons of rosiglitazone-treated mice as compared to control mice. Also, serum amyloid P component (SAP) concentrations in plasma were increased. However, concentrations of tumor necrosis factor (TNF)-α and interferon (IFN)-γ in colon homogenates, and TNF-α in spleen homogenates were significantly decreased, whereas interleukin (IL)-10 in spleen homogenates was increased. Other cytokines (IL-2, IL-4, IL-6, IL-12p70 and monocyte chemotactic protein (MCP)-1) and myeloperoxidase (MPO) concentrations showed no differences. In conclusion, 16 days pretreatment with rosiglitazone impaired DSS-induced colitis in mice.

Expression of peroxisome proliferator-activated receptor-gamma in macrophage suppresses experimentally induced colitis

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) has been shown to be a protective transcription factor in mouse models of inflammatory bowel disease (IBD). PPAR-gamma is expressed in several different cell types, and mice with a targeted disruption of the PPAR-gamma gene in intestinal epithelial cells demonstrated increased susceptibility to dextran sulfate sodium (DSS)-induced IBD. However, the highly selective PPAR-gamma ligand rosiglitazone decreased the severity of DSS-induced colitis and suppressed cytokine production in both PPAR-gamma intestinal specific null mice and wild-type littermates. Therefore the role of PPAR-gamma in different tissues and their contribution to the pathogenesis of IBD still remain unclear. Mice with a targeted disruption of PPAR-gamma in macrophages (PPAR-gamma(DeltaMphi)) and wild-type littermates (PPAR-gamma(F/F)) were administered 2.5% DSS in drinking water to induce IBD. Typical clinical symptoms were evaluated on a daily basis, and proinflammatory cytokine analysis was performed. PPAR-gamma(DeltaMphi) mice displayed an increased susceptibility to DSS-induced colitis compared with wild-type littermates, as defined by body weight loss, diarrhea, rectal bleeding score, colon length, and histology. IL-1beta, CCR2, MCP-1, and inducible nitric oxide synthase mRNA levels in colons of PPAR-gamma(DeltaMphi) mice treated with DSS were higher than in similarly treated PPAR-gamma(F/F) mice. The present study has identified a novel protective role for macrophage PPAR-gamma in the DSS-induced IBD model. The data suggest that PPAR-gamma regulates recruitment of macrophages to inflammatory foci in the colon.

Rosiglitazone, a PPARgamma ligand, modulates signal transduction pathways during the development of acute TNBS-induced colitis in rats

Recent studies have shown that peroxisome proliferator-activated receptor gamma (PPARgamma), a highly nuclear receptor expressed in the colon, may participate in the control of inflammation, especially in regulating the production of immunomodulatory and inflammatory mediators, cellular proliferation and apoptosis. In order to delve into the anti-inflammatory mechanisms and signalling pathways of PPARgamma agonists, we have studied the effects of rosiglitazone, a PPARgamma agonist on the extent and severity of acute ulcerative colitis caused by intracolonic administration of 2,4,6-trinitribenzene sulfonic acid (TNBS) in rats. The inflammatory response was assessed by gross appearance, myeloperoxidase (MPO) activity, tumour necrosis factor alpha (TNF-alpha) levels and a histological study of the lesions. We determined prostaglandin E2 production as well as the cyclooxygenases (COX)-1 and -2 expressions by immunohistochemistry and Western blotting. The nuclear factor kappa (NF-kappaB) p65 and p38 mitogen-activated protein kinase (MAPK) expression levels were also measured by Western blotting. Finally, since PPARgamma agonists modulate apoptosis, we tried to clarify its effects under early acute inflammatory conditions. Inflammation following TNBS induction was characterized by increased colonic wall thickness, edema, diffuse inflammatory cells infiltration, necrosis reaching an ulcer index (UI) of 9.66+/-0.66 cm(2) and increased MPO activity and TNF-alpha colonic levels. Rosiglitazone treatment significantly reduced the morphological alteration associated with TNBS administration and the UI with the highest dose. In addition, the degree of neutrophil infiltration and the cytokine levels were significantly ameliorated. Rosiglitazone significantly reduced the rise in the prostaglandin (PG) E(2) generation compared with TNBS group. The COX-1 levels remained stable throughout the treatment in all groups. The COX-2 expression was elevated in TNBS group; however rosiglitazone administration reduced the COX-2 overexpression. A high expression of NF-kappaB p65 and p38 MAPK proteins appeared in colon mucosa from control TNBS-treated rats; nevertheless, PPARgamma agonist treatment drastically decreased them. There were no significant changes in apoptosis after rosiglitazone treatment when compared to TNBS group. In conclusion, rosiglitazone seems to modulate the acute colitis through NF-kappaB p65 and p38 MAPK signalling pathways.

Hydrolyzed Protein Diets for Dogs and Cats

The primary aim of a hydrolyzed protein diet is to disrupt the proteins within the diet sufficiently to remove existing allergens. Published assessment of hydrolyzed protein diets includes physiochemical and immunologic assays as well as nutritional and clinical feeding trials. Potential problems include poor palatability, hypoosmotic diarrhea, and a reduced nutritional value, although persistent allergenicity is the most significant. The primary indications for a hydrolyzed protein diet are use in elimination trials for the diagnosis of adverse food reactions, and the initial management of inflammatory bowel disease. Initial studies of hydrolyzed diet efficacy are encouraging. Consideration of the source ingredients should be given when using hydrolyzed protein diets in elimination feeding trials because antigenic sites may not be fully destroyed.

The long and winding road to gut homeostasis

PURPOSE OF REVIEW

The open ecosystem of the alimentary tract, harboring approximately 1 kg of bacteria, exhibits a rapid, but tightly controlled turnover. Impaired nuclear receptor function can give rise to perturbation in the gut, leading to inflammation and possibly neoplasia. Intriguingly, bacteria-dependent signaling pathways can modulate, and in turn be modulated by, a subset of nuclear receptors. This review attempts to highlight how microbes and nuclear receptors could jointly regulate gut homeostasis.

RECENT FINDINGS

Commensal bacteria can utilize peroxisome proliferator activated receptor-gamma-dependent nuclear export of RelA as a novel mechanism to attenuate inflammatory signals triggered by a pathogen. Other nuclear receptors, such as liver X receptor, vitamin D receptor and farnesoid X receptor were also recently shown to interact with bacteria-induced mammalian inflammatory pathways. Although details of this interplay are still being unraveled, a role for these and other nuclear receptors in gastrointestinal inflammation and possibly neoplasia is beyond dispute.

SUMMARY

The commensal microflora is being accorded due importance in regulating homeostasis of the gastrointestinal tract. Recent data suggest that the molecular messengers used by these bacteria include nuclear receptors. Exploiting mechanisms of nuclear receptor activity as drug targets, together with a detailed knowledge of the microbiota, could improve our understanding of gut-related ailments, and aid in mitigating their symptoms.

Treatment of murine Th1- and Th2-mediated inflammatory bowel disease with NF-kappa B decoy oligonucleotides

The Th1 and Th2 T cell responses that underlie inflammatory bowel diseases (IBDs) are likely to depend on NF-kappaB transcriptional activity. We explored this possibility in studies in which we determined the capacity of NF-kappaB decoy oligodeoxynucleotides (decoy ODNs) to treat various murine models of IBD. In initial studies, we showed that i.r. (intrarectal) or i.p. administration of decoy ODNs encapsulated in a viral envelope prevented and treated a model of acute trinitrobenzene sulfonic acid-induced (TNBS-induced) colitis, as assessed by clinical course and effect on Th1 cytokine production. In further studies, we showed that NF-kappaB decoy ODNs were also an effective treatment of a model of chronic TNBS-colitis, inhibiting both the production of IL-23/IL-17 and the development of fibrosis that characterizes this model. Treatment of TNBS-induced inflammation by i.r. administration of NF-kappaB decoy ODNs did not inhibit NF-kappaB in extraintestinal organs and resulted in CD4+ T cell apoptosis, suggesting that such treatment is highly focused and durable. Finally, we showed that NF-kappaB decoy ODNs also prevented and treated oxazolone-colitis and thus affect a Th2-mediated inflammatory process. In each case, decoy administration led to inflammation-clearing effects, suggesting a therapeutic potency applicable to human IBD.

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.

Chronic inflammatory disorders of the gastrointestinal tract of companion animals

In the inflammatory bowel diseases (IBD) that affect dogs and cats there appears to be dysregulation of normal mucosal immunity, characterised by polyclonal lymphocytic infiltrates which are presumably specific for luminal antigens. There is an absence of a classical polarisation of either T-helper (Th) 1 or Th2 cytokine responses, although increased expression of mRNA for interleukin (IL) 2 and IL-12p40 and a shift towards mucosal immunoglobulin (Ig) G production are consistent findings, whilst variable responses are seen in tumour necrosis factor-alpha (TNF-alpha), IL-1, IL-4, IL-6, and interferon-gamma (IFN-gamma). Increased mucosal permeability and deranged intestinal motility are common sequelae. Despite obvious similarities with Crohn's disease and ulcerative colitis in humans, important differences exist. Of these, the diffuse superficial nature but with no Th1 or Th2 bias, and the prevalence of proximal small intestinal disease are notable. Potential hypotheses for these disparities include specific differences in the types or locations of agonistic gut flora, diffuse abnormalities in microbial-host interactions, a greater importance of diet, or anatomical or cellular differences in mucosal immune responses. Although specific pathogens and genetic susceptibilities may be involved, quantitative or qualitative changes in the normal flora or abnormal responses to a normal flora are more likely to be involved in the immunopathogenesis. Dietary influences include a large source of antigen, promotion of abnormal microbial growth through Maillard compounds within canned diets, and specific macro- and micronutrient deficiencies. Although dependent on a histopathological diagnosis, limitations of biopsies procured endoscopically, lack of histopathological standardisation and difficulty distinguishing inflammation from neoplasia remain significant problems. Clinician-pathologist dialogue, immunohistochemistry, cytokine profiling and lymphocyte clonality assessment may lead to more accurate diagnoses, a deeper understanding of the immunopathogenesis, and ultimately to new therapies or prevention of disease induction.

Partially hydrolyzed guar gum down-regulates colonic inflammatory response in dextran sulfate sodium-induced colitis in mice

Partially hydrolyzed guar gum (PHGG), a water-soluble dietary fiber produced by a controlled partial enzymatic hydrolysis of guar gum beans, has various physiological actions. The aim of the present study was to elucidate the beneficial effects of PHGG on colonic mucosal damage and on the inflammatory response in a dextran sulfate sodium (DSS) colitis model. After 2 weeks of prefeeding of PHGG, acute colitis was induced with 8% DSS in female BALB/c mice. Colonic mucosal inflammation was evaluated clinically, biochemically and histologically. Mucosal protein contents and mRNA levels of tumor necrosis factor-alpha (TNF-alpha) were determined by immunoassay and reverse transcription polymerase chain reaction. Disease activity scores determined by weight loss, stool consistency and blood in stool in DSS-treated mice were significantly lower in the PHGG-treated mice compared with the control mice. Shortening of the colon was significantly reversed by PHGG. Histological study also showed a reduced infiltration of inflammatory cells, especially neutrophils, and mucosal cell disruption in PHGG-treated mice compared with the control mice. The increases in tissue-associated myeloperoxidase activity and thiobarbituric acid-reactive substances after DSS administration were both significantly inhibited by pretreatment with PHGG. Partially hydrolyzed guar gum also inhibited increases in intestinal TNF-alpha protein and mRNA expression after DSS administration, respectively. These results suggest that chronic ingestion of PHGG prevents the development of DSS-induced colitis in mice via the inhibition of mucosal inflammatory response.

A PPAR-gamma ligand, 15-deoxy-Delta12,14-prostaglandin J(2), inhibited gastric mucosal injury induced by ischemia-reperfusion in rats

INTRODUCTION

Recent studies have demonstrated the anti-inflammatory action of 15-deoxy-Delta12,14-prostaglandin J(2) (15d-PGJ(2)), a derivative of the PGD(2) metabolic pathway. Acute inflammation, including neutrophil activation, plays a critical role in the pathogenesis of ischemia-reperfusion (I/R). The aim of the present study was to determine the effect of 15d-PGJ(2) on I/R-induced gastric mucosal injury in rats.

METHODS

Gastric mucosal damage was induced in male Wistar rats by clamping the celiac artery for 30 min followed by reperfusion. 15d-PGJ(2) (0.01-1.0 mg/kg) was given to the rats intraperitoneally 1 h before the vascular clamping. The area of gastric mucosal erosions (erosion index) was measured. Thiobarbituric acid reactive substances (TBARS) and tissue-associated myeloperoxidase (MPO) activity were measured in the gastric mucosa as indices of lipid peroxidation and neutrophil infiltration. The expression of tumor necrosis factor-alpha (TNF-alpha) in gastric mucosa was measured by ELISA. In addition, to elucidate whether the protective effects of 15d-PGJ(2) are related to the activation of the PPAR-gamma receptor, we also investigated the effects of a PPAR-gamma antagonist, GW9662.

RESULTS

After 60 min of reperfusion, the area of gastric erosion index had significantly increased from the mean basal levels. The increase in the erosion index was significantly inhibited by pretreatment with 15d-PGJ(2) in a dose-dependent manner. On the other hand, GW9662 reversed the protective effect of 15d-PGJ(2). The concentration of TBARS and MPO activity in the gastric mucosa were both significantly increased after I/R, and pretreatment with 15d-PGJ(2) significantly reduced these increases. The TNF-alpha content was significantly higher in the I/R group than in the sham-operated group. However, the increase in TNF-alpha was significantly inhibited by pretreatment with 15d-PGJ(2).

CONCLUSIONS

15d-PGJ(2) significantly inhibited the severity of acute gastric mucosal injury induced by I/R in rats through PPAR-gamma-dependent mechanisms. This effect may be due, in part, to a reduction in the infiltration of neutrophils into the gastric mucosa, possibly via the inhibition of inflammatory cytokine.

Rosiglitazone, an agonist of peroxisome proliferator-activated receptor gamma, reduces chronic colonic inflammation in rats

Recent studies have shown the implication of the peroxisome proliferator-activated receptor gamma (PPARgamma) in control of inflammation, immune and apoptotic responses during early experimental colitis. However, there is little information about the effects of these agents on colonic mucosa under chronic inflammatory conditions. In this study, we have evaluated the effects of rosiglitazone, a PPAR-gamma agonist, on the chronic injury caused by intra-colonic administration of trinitrobenzensulfonic acid (TNBS) in rats. Rosiglitazone (1 and 5mg/kg p.o.) was administered by oral gavage, 24h after TNBS instillation and daily during 2 weeks before killing the rats. Colons were removed for histological and biochemical analysis. Administration of rosiglitazone corrected the disorders in morphology associated to lesions, significantly reduced the ulceration index, the rise of myeloperoxidase (MPO) and the levels of tumour necrosis factor alpha (TNF-alpha). In addition, rosiglitazone treatment increased prostaglandin (PG)E(2) production and returned PGD(2) to basal levels. Also, reduced cyclooxygenase (COX)-2 and nuclear transcription factor NF-kappa B (NF-kappaB) p65 proteins expression. Furthermore, treatment of rats with rosiglitazone caused a significant increase of TNBS-induced apoptosis. In summary, rosiglitazone exerts protective effects in chronic experimental colitis. The anti-inflammatory effects seem to be related to impairment of neutrophil function, absence of up-regulation of TNF-alpha and decrease of nuclear NF-kappaB p65 expression. Our results also suggest that the activation of the PPARgamma pathway reduces COX-2 overexpression, returns the increased PGD(2) values to basal levels and induces a significant increase of TNBS-induced apoptosis. We conclude that rosiglitazone represents a novel approach to the treatment of ulcerative colitis.

Intestinal antiinflammatory effects of thiazolidenedione peroxisome proliferator-activated receptor-gamma ligands on T helper type 1 chemokine regulation include nontranscriptional control mechanisms

Crohn's disease is associated with an excessive T helper (TH) type 1 inflammatory immune response. Reducing the influx of disease-associated CD4+ TH1 cells into the inflamed intestine is likely to be beneficial in preventing a disease flare-up and even possibly in reducing the effect of acute disease. Thiazolidenedione (TZD) ligands, which activate peroxisome proliferator-activated receptor-gamma (PPARgamma), have been shown to reduce TH1 inflammation in murine models of colitis, primarily in a preventative fashion. To determine whether PPARgamma ligands reduce this inflammation in part by reducing TH1 chemoattractant levels in vivo, the TZD pioglitazone was tested for its effects on a TH1 chemokine (CXCL10) in 2 models of colitis (i.e., dextran sodium sulfate and 2,4,6-dinitrobenzene sulfonic acid-mediated colitis). In both models, CXCL10 levels were significantly reduced by pioglitazone. Because TZDs can affect gene expression either directly, by regulating the binding of PPARgamma to consensus promoter elements, or indirectly, by modulating other signaling pathways that can affect gene transcription, the regulation of CXCL10 by TZDs was investigated in vitro in both HT-29 colon epithelial cells and THP-1 monocyte/macrophage cells. TZDs significantly reduced CXCL10 protein levels from activated HT-29 cells and THP-1-derived macrophages in a dose-dependent manner at nanomolar concentrations. However, TZDs did not affect messenger RNA levels or nuclear factor-kappaB activation at these concentrations in these cells. These findings imply the existence of a novel posttranscriptional regulatory antiinflammatory mechanism by TZDs that is not associated with reductions in nuclear factor-kappaB activation.

Inhibitory effect of pioglitazone on expression of adhesion molecules on neutrophils and endothelial cells

The interaction between leukocytes and the vascular endothelial cells (EC) via cellular adhesion molecules plays an important role in various inflammatory and immune diseases. It has been suggested that peroxisome proliferator-activated receptor-gamma (PPAR-gamma, a member of the nuclear receptor superfamily of transcription factors) might be involved in the control of inflammation and in modulating the expression of various cytokines. The aim of this investigation was to evaluate the anti-inflammatory properties of PPAR-gamma activators, as well as the inhibitory effect of PPAR-gamma on the expression of adhesion molecules on leukocytes and vascular endothelial cells. Pioglitazone, a synthetic PPAR-gamma activator, suppressed the increase of CD11b/CD18 expression on FMLP-activated leukocytes, as detected by immunofluorescence flow cytometry. However, the FMLP-induced elevation of cytosolic Ca2+ in leukocytes was not suppressed by pioglitazone. Pioglitazone inhibited the expression of VCAM-1 protein and mRNA on activated human umbilical vein endothelial cells (HUVEC) after IL-1beta stimulation, as detected by ELISA and real-time PCR. However, it showed little effect on the expression of ICAM-1 and E-selectin. The present study revealed that pioglitazone can influence monocyte-EC binding by inhibiting VCAM-1 expression on activated EC and neutrophil-EC binding by inhibiting upregulation of CD11b/CD18 on activated neutrophils. Accordingly, pioglitazone may be useful for treating inflammatory diseases.