Table of Contents Author Guidelines Submit a Manuscript
PPAR Research
Volume 2010 (2010), Article ID 108632, 8 pages
http://dx.doi.org/10.1155/2010/108632
Review Article

Gastrointestinal Cytoprotection by PPAR Ligands

Molecular Gastroenterology and Hepatology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, 465 Kajii-cho, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan

Received 29 April 2010; Accepted 23 August 2010

Academic Editor: Paul Drew

Copyright © 2010 Yuji Naito et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Peroxisome proliferator-activated receptor (PPAR ) 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, PPAR 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 PPAR ligands in the gastrointestinal tract.

1. Introduction

Peroxisome proliferator-activated receptors (PPARs) are transcription factors belonging to the nuclear receptor superfamily and have been initially described as molecular targets for compounds that cause peroxisome proliferation [1]. Thus far, 3 isotypes of PPARs ( , (also known as ), and ) have been found in various species [25]. Of these, proved to be a key transcription factor involved in lipid metabolism and adipocyte differentiation. In addition, recent studies suggest that may be involved in the control of inflammation and especially modulation of the expression of various cytokines in monocytes and macrophages [6, 7]. Regarding the anti-inflammatory properties of , activation has been shown to antagonize the activity of activation protein-1 (AP-1), Stat 1, and nuclear factor- B (NF- B), which are known for positively controlling cytokine gene expression [6].

predominates the adipose tissue, large intestine, macrophages, and monocytes [6, 810]. Recently, it was demonstrated that 15-deoxy- 12, 14-prostaglandin J2 (15d-PGJ2), and various polyunsaturated fatty acids have been identified as natural receptor ligands of . In addition, thiazolidinediones such as troglitazone, pioglitazone, and rosiglitazone, which are used as antidiabetic drugs, have been developed as synthetic ligands. The use of such ligands has allowed researchers to unveil many potential roles of PPARs in pathological conditions, including atherosclerosis, inflammation, and cancer. In this paper, we present the current knowledge available on the role of in the gastrointestinal tract.

2. Esophagus and PPAR

Few studies have examined the role of in the esophageal mucosa. expression in the epithelium of Barrett’s esophagus (BE) is elevated as compared to that in the normal esophageal squamous epithelium [11]. Reflux of gastric juice or bile acid into the esophagus causes injury to the esophageal squamous epithelium, because of which the injured esophageal mucosa is replaced by columnar epithelium; this entity is called BE. Importantly, BE is the major risk factor for esophageal adenocarcinoma. The ligands pioglitazone and ciglitazone when used alone inhibited cell proliferation in OE33 cells derived from esophageal adenocarcinoma [11, 12]; this result suggests that plays an important role in Barrett’s carcinogenesis and that ligands may be useful as new therapeutic agents for the prevention and treatment of Barrett’s carcinoma. However, because it has been reported that OE33-derived transplantable adenocarcinoma was enhanced in vivo by systemic activation due to cell proliferation, the detailed role of in the esophagus remains controversial [11].

In regard to human esophageal squamous cell carcinoma (SCC), has been found to be expressed in human SCC cell lines such as TE-1, TE-2, TE-5, TE-7, TE-8, TE-9, and TE-10 [13, 14]. Interestingly, ligands such as 15-deoxy- 12,14-prostaglandin J2 (15d-PGJ2), and troglitazone significantly inhibited the proliferation of these SCC cells in a dose-dependent manner [13]. On the other hand, Terashita et al. reported that although mRNA expression was detectable in the majority of human SCC tissues and all the normal esophageal mucosa, mRNA expression level was significantly decreased in SCC tissues compared to normal esophageal mucosa [14]. In their clinicopathological studies, mRNA expression level in the patients with esophageal SCC with extensive lymph node metastasis was significantly decreased compared with those with less extensive lymph node metastasis. Thus, the role of remains controversial in esophageal SCC as well as esophageal adenocarcinoma, and further examinations is required to gain a better understanding of the role of in esophageal tumors.

3. Stomach and PPAR

In several studies, it has been demonstrated that ligands reduced the extent of mucosal damage and inhibited the inflammatory response to gastric inflammation (Table 1). First, we demonstrated that pioglitazone, a specific ligand, ameliorated aspirin-induced injury to the gastric mucosa in rats (Figure 1) and inhibited the increase in neutrophil accumulation associated with gastric mucosal TNF- contents, which were measured by Enzyme-Linked Immunosorbent Assay (ELISA) [15]. has also been implicated in the control of gastric mucosal damage induced by ischemia-reperfusion injury [16]. Pioglitazone, rosiglitazone, troglitazone, and 15d-PGJ2 inhibited gastric mucosal damage induced by ischemia-reperfusion injury through the inhibition of cytokines expression such as TNF- and IL-1 and the inhibition of the neutrophil accumulation in the gastric mucosa [1621]. Interestingly, regarding the expression of intercellular adhesion molecule-1 (ICAM-1), which played an important role in neutrophil infiltration into gastric mucosa, the increased expression of ICAM-1 after gastric ischemia reperfusion was also inhibited by treatment with these ligands [18, 21]. Thus, mediated the amelioration of the inflammatory responses involved in acute gastric damage.

tab1
Table 1: Cytoprotective properties of in experimental model of gastric injuries.
fig1
Figure 1: Effect of increasing doses of pioglitazone on acute gastric mucosal injury induced by aspirin-HCl in rats (a) The effect of pioglitazone on tissue-associated myeloperoxidase (MPO) activity (b) and TNF- content (c) induced by aspirin-HCl in the gastric mucosa. TNF- content and MPO activity in the gastric mucosa increased after aspirin administration. This increase in TNF- content and MPO activity was inhibited by pioglitazone treatment.

In gastric ulcer healing, it seems that the activation of ligands produces favorable effects. Pioglitazone accelerates the healing of acetic acid-induced gastric ulcers by the triggering anti-inflammatory effects, including the suppression of interleukin (IL)-1 tumor necrosis factor- (TNF- , cyclooxygenase (COX)-2, and inducible nitric oxide synthase (iNOS), and by increasing the expression of heat shock protein 70 (HSP70) [23]. Brzozowski et al. also demonstrated that pioglitazone accelerates the healing of gastric ulcers induced by topical application of 100% ethanol or water immersion and restraint stress [24]. In addition to suppression of the proinflammatory cytokines TNF- and interleukin-1 (IL-1 pioglitazone enhanced angiogenesis through increased expression of platelet endothelial cell adhesion molecule-1 (PECAM-1)). Furthermore, Lahiri et al. also reported that pioglitazone-induced activation of mediated gastric ulcer healing in rats, and this pioglitazone-mediated gastroprotective effect is also involved in glucocorticoid receptor activation during chronic gastric ulcer healing [22]. Hence, together the data suggest that is a novel therapeutic target molecule and ligands can be used as therapeutic agents for gastric ulcerative lesion.

Interestingly, plays a crucial role in gastric mucosal injury in relation to H. pylori (Helicobacter pylori) infection. As It has been well known that Helicobacter pylori infection plays important role as the cause of chronic gastritis [37] and as a definite carcinogen in gastric cancer [38], understanding how is involved in H. pylori infection may lead to the development of therapeutic strategy for H. pylori infection. B. L. Slomiany and A. Slomiany have demonstrated that H. pylori lipopolysaccharide- (LPS-) elicited mucosal inflammatory responses were accompanied by a massive epithelial cell apoptosis, upregulation of iNOS, and COX-2 expression, and ligand ciglitazone suppresses these gastric mucosal inflammatory responses and may provide therapeutic benefits such as the amelioration of inflammation associated with H. pylori infection [39]. In fact, expression in the gastric mucosa increases with H. pylori infection and produces cytoprotective and anti-inflammatory effects in the gastric mucosa [40]. Furthermore, Konturek et al. also have shown that is implicated in H. pylori-related gastric carcinogenesis and that agonists may have a therapeutic role in cancer [41]. On experimental investigation, it was found that suppresses gastric carcinogenesis and that ligands such as troglitazone and ciglitazone are potential agents for gastric carcinoma because they inhibit -dependant cell proliferation [4244].

On the other hand, the importance of polymorphism (Pro12Ala) has been reported. The Pro12Ala polymorphism has been reported to show decreased binding to the promoter element and demonstrates weaker transactivation of responsive promoters [45]. It has been reported that polymorphism (Pro12Ala) is associated with various disease including diabetes, asthma, endometriosis, polycystic ovary, and colorectal cancer [4650]. Regarding to gastric disease, this polymorphism is associated with not only gastric ulcer but also gastric adenocarcinoma [5153].

4. Intestine and PPAR

In many studies, has been reported to play a role in the small and large intestine. This is probably because of high expression in the colon tissue. The high expression of seems to be related to intestinal bacteria. Dubuquoy et al. showed that expression in the colon tissue was greater in conventional mice than in germ-free mice [54]. More interestingly, they demonstrated that expression was weaker in the colon tissue of mice deleted for the Toll-like receptor (TLR4) than in that of wild-type mice. Furthermore, in colonic epithelial cells such as HT-29 and Caco-2, expression was markedly increased because of the presence of LPSs [55]. These data indicate that the role of bacteria-derived LPS in the regulation of PPAR expression is more crucial in the colon tissue than in other parts of the gastrointestinal tract.

With regard to the anti-inflammatory properties of P in intestinal inflammation, the therapeutic efficacy of ligands has been evaluated in various different models of intestinal inflammation (Table 2). To determine the role of in intestinal ischemia-reperfusion injury, Nakajima et al. [18] used -deficient mice and the agonist rosiglitazone. They demonstrated the dramatic protective effects of rosiglitazone on both local and remote organ injury after intestinal ischemia-reperfusion injury and showed that the endogenous absence of leads to aggravated injury in this model. In several studies, it has been demonstrated that the activation of by ligands inhibited intestinal ischemia-reperfusion injury [25, 26, 56]. One possible mechanism by which activation helps in protection against ischemia-reperfusion injury is through the inhibition of NF- B-mediated transcription. The inhibition of NF- B activation was confirmed by several approaches, including electrophoretic mobility shift assays, immunohistochemistry using a phosphorylation state-specific antibody for I B, and mRNA levels of TNF- and intercellular adhesion molecule-1 (ICAM-1), which are downstream targets of NF- B.

tab2
Table 2: Cytoprotective properties of PPAR in experimental model of the intestinal inflammation.

Inflammatory bowel diseases (IBDs) such as ulcerative colitis (UC) and Crohn’s disease (CD) constitute chronic and recurrent intestinal inflammatory disorders; the precise pathogenesis of these disorders remains unknown [57]. Therefore, it is very important to identify novel therapeutic molecules for IBDs. In this regard, may be a novel therapeutic target. Su et al. showed that ligands markedly reduced colonic inflammation in a mouse model of IBD [27]. We also reported that pioglitazone had a protective effect against murine dextran sulfate sodium- (DSS-) induced colitis; a model of colitis induced in this manner is commonly used as a UC model in association with inhibition of the NF- B-cytokine cascade [29] (Figure 2). In mice, overexpression of by an adenoviral construct in mucosal epithelial cells was associated with amelioration of experimental inflammation [58], and this study supports the hypothesis that the upregulation of expression itself may have a protective effect against colitis. In another study, in which colitis was induced by trinitrobenzene sulfonic acid (TNBS) and used as a CD model, ligands such as pioglitazone [30], rosiglitazone [33], and troglitazone [32] inhibited the development of the intestinal inflammation.

fig2
Figure 2: (a) Image showing the appearance of the colon in a mouse that was administered dextran sulfate sodium (DSS) (i) and pioglitazone (ii). Loss and shortening of crypts, mucosal erosions, inflammatory cell infiltration, and goblet cell depletion are seen in (i). In (ii), smaller erosions are associated with less inflammatory cell infiltration. Hematoxylin and eosin staining, Effects of pioglitazone on mRNA expression of TNF- (b) and on DNA-binding activity of NF- B (c) in colonic tissues of mice that were administered DSS. Reverse transcriptase-polymerase chain reaction (RT-PCR), electrophoresis mobility shift assay (EMSA) of sham-operated colon (lane 1), DSS-induced inflamed tissue (lane 2), colon treated with 3 mg/kg pioglitazone (lane 3), and sham-operated colon treated with pioglitazone (lane 4). TNF- mRNA and NF- B DNA-binding activity were upregulated in inflamed colonic tissue (lane 2); this upregulation was suppressed by pioglitazone administration (lane 3).

DSS-induced and TNBS-induced colitis are widely used models of chemically induced intestinal inflammation. In studies on immune-reactive cells in the intestinal tissue of UC and CD patients, it has been demonstrated that the deregulated immune response plays a crucial role in the onset of IBD. Therefore, other types of colitis models are widely used, including a transfer colitis model produced by transfer of a T-cell population ( CD45RBhigh T cells) that lacks regulatory cells into an immunodeficient host, spontaneous colitis model such as the SAMP/Yit mouse, and genetic colitis model such as interleukin IL-10-deficient mice. In a previous study, it was found that rosiglitazone delayed the onset of colitis in IL-10-deficient mice [35]. Further, it was also found that crypt hyperplasia, caused by increased mitotic activity of crypt epithelial cells, was also delayed by rosiglitazone accompanied by the decreased expression of interferon- (IFN- ), IL-17, TNF- and iNOS in the colon. Sugawara et al. have identified as a CD susceptibility gene in both mice and humans [36]. The administration of rosiglitazone inhibited SAMP/Yit ileitis through regulation of activity in the crypts of the small intestine.

With regard to the relation between immune cells and it has been reported that ligands modulate dendritic cell (DC) function to elicit the development of anergic T cells [59]. Hontecillas and Bassaganya-Riera demonstrated that effector cell function was downregulated by activated regulatory T cells (Tregs), which were activated by endogenously produced [60]. In fact, they also showed that deficiency in Tregs impairs the ability of Tregs to prevent T-cell transfer-induced colitis. With regard to the transfer colitis model, Bassaganya-Riera et al. showed that conjugated linoleic acid ameliorated colitis [31].

Thus, ligands reduced mucosal damage and prevented or downregulated the inflammatory response in several murine models of intestinal inflammation. These anti-inflammatory effects suggest that agonists may provide a novel therapeutic approach for treating IBD. In fact, rosiglitazone produced beneficial effects in the treatment of UC in an open-label trial [61]. In this study, rosiglitazone treatment for UC patients refractory to conventional treatment yielded a decrease in disease activity index score. Although the results of this pilot study are yet to be confirmed, ligands may be novel therapeutic agents for treating IBD.

More interestingly, Rousseaux et al. showed that the therapeutic effect of 5-aminosalicylic acid (5-ASA) may be mediated by [34]. Heterozygous -knockout mice were refractory to 5-ASA treatment, and 5-ASA directly induced expression in colonic epithelial cells in vitro. Although 5-ASA is one of the conventional agents uses for IBD treatment, the precise mechanism underlying the protective effect of 5-ASA remained unclear. These data reveal that is a target of 5-ASA; this finding underlies the anti-inflammatory effects produced in the colon.

Many studies have investigated the relation between and colon cancer. is expressed at high levels in primary colon tumors and colon cancer cell lines [62]. On the other hand, ligands cause withdrawal of colon cancer cell lines from the cell cycle, inhibit cell growth, and promote differentiation [63, 64]. Based on these finding, it appears as if may be exerting some other actions rather than regulating tumor growth. One possibility is that expression by the tumor may program these cells to be less immunogenic or possibly lead to the secretion of molecules that would end up promoting tumor growth. Osawa et al. recently showed that continuous feeding of pioglitazone reduced the aberrant crypt foci formation and notably suppressed colon tumors [65]. Although there is a contradictory study in which mice showed an increased number of polyps when subjected to a agonist [66], many research studies have shown that agonists seem to have inhibitory effects on the proliferation of colon cancer cells. ligands may represent a new group of biological agents that can be used for the management of colon cancer.

5. Conclusion

In this paper, we focused on the therapeutic effect of agonists in gastrointestinal inflammation. We performed studies using several animal models of gastrointestinal inflammation and accumulated evidence suggesting that plays a crucial role in gastrointestinal inflammation. It was found that ligand therapy reduced a wide variety of inflammatory indices in different animal models, but the underlying mechanism by which activation produces these effects was not fully established. We expect that the precise mechanism by which ligands produce anti-inflammatory properties will be clarified in the near future.

References

  1. D. J. Mangelsdorf, C. Thummel, M. Beato et al., “The nuclear receptor super-family: the second decade,” Cell, vol. 83, no. 6, pp. 835–839, 1995. View at Google Scholar · View at Scopus
  2. T. Sher, H.-F. Yi, O. W. McBride, and F. J. Gonzalez, “cDNA cloning, chromosomal mapping, and functional characterization of the human peroxisome proliferator activated receptor,” Biochemistry, vol. 32, no. 21, pp. 5598–5604, 1993. View at Google Scholar · View at Scopus
  3. A. Schmidt, N. Endo, S. J. Rutledge, R. Vogel, D. Shinar, and G. A. Rodan, “Identification of a new member of the steroid hormone receptor superfamily that is activated by a peroxisome proliferator and fatty acids,” Molecular Endocrinology, vol. 6, no. 10, pp. 1634–1641, 1992. View at Publisher · View at Google Scholar · View at Scopus
  4. A. Elbrecht, Y. Chen, C. A. Cullinan et al., “Molecular cloning, expression and characterization of human peroxisome proliferator activated receptors γ1 and γ2,” Biochemical and Biophysical Research Communications, vol. 224, no. 2, pp. 431–437, 1996. View at Publisher · View at Google Scholar · View at Scopus
  5. L. Fajas, D. Auboeuf, E. Raspé et al., “The organization, promoter analysis, and expression of the human PPARγ gene,” Journal of Biological Chemistry, vol. 272, no. 30, pp. 18779–18789, 1997. View at Publisher · View at Google Scholar · View at Scopus
  6. M. Ricote, A. C. Li, T. M. Willson, C. J. Kelly, and C. K. Glass, “The peroxisome proliferator-activated receptor-γ is a negative regulator of macrophage activation,” Nature, vol. 391, no. 6662, pp. 79–82, 1998. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  7. C. Jiang, A. T. Ting, and B. Seed, “PPAR-γ agonists inhibit production of monocyte inflammatory cytokines,” Nature, vol. 391, no. 6662, pp. 82–86, 1998. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  8. D. Auboeuf, J. Rieusset, L. Fajas et al., “Tissue distribution and quantification of the expression of mRNAs of peroxisome proliferator-activated receptors and liver X receptor-α in humans: no alteration in adipose tissue of obese and NIDDM patients,” Diabetes, vol. 46, no. 8, pp. 1319–1327, 1997. View at Google Scholar · View at Scopus
  9. N. Marx, U. Schönbeck, M. A. Lazar, P. Libby, and J. Plutzky, “Peroxisome proliferator-activated receptor gamma activators inhibit gene expression and migration in human vascular smooth muscle cells,” Circulation Research, vol. 83, no. 11, pp. 1097–1103, 1998. View at Google Scholar · View at Scopus
  10. R. Mukherjee, L. Jow, D. Noonan, and D. P. McDonnell, “Human and rat peroxisome proliferator activated receptors (PPARs) demonstrate similar tissue distribution but different responsiveness to PPAR activators,” Journal of Steroid Biochemistry and Molecular Biology, vol. 51, no. 3-4, pp. 157–166, 1994. View at Publisher · View at Google Scholar · View at Scopus
  11. O. H. Al-Taie, T. Graf, B. Illert et al., “Differential effects of PPARγ activation by the oral antidiabetic agent pioglitazone in Barrett's carcinoma in vitro and in vivo,” Journal of Gastroenterology, vol. 44, no. 9, pp. 919–929, 2009. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  12. P. C. Konturek, A. Nikiforuk, J. Kania, M. Raithel, E. G. Hahn, and S. M. Mühldorfer, “Activation of NFκB represents the central event in the neoplastic progression associated with Barrett's esophagus: a possible link to the inflammation and overexpression of COX-2, PPARγ and growth factors,” Digestive Diseases and Sciences, vol. 49, no. 7-8, pp. 1075–1083, 2004. View at Publisher · View at Google Scholar · View at Scopus
  13. T. Takashima, Y. Fujiwara, M. Hamaguchi et al., “Relationship between peroxisome proliferator-activated receptor-gamma expression and differentiation of human esophageal squamous cell carcinoma,” Oncology Reports, vol. 13, no. 4, pp. 601–606, 2005. View at Google Scholar · View at Scopus
  14. Y. Terashita, H. Sasaki, N. Haruki et al., “Decreased peroxisome proliferator-activated receptor gamma gene expression is correlated with poor prognosis in patients with esophageal cancer,” Japanese Journal of Clinical Oncology, vol. 32, no. 7, pp. 238–243, 2002. View at Publisher · View at Google Scholar · View at Scopus
  15. Y. Naito, T. Takagi, K. Matsuyama, N. Yoshida, and T. Yoshikawa, “Pioglitazone, a specific PPAR-γ ligand, inhibits aspirin-induced gastric mucosal injury in rats,” Alimentary Pharmacology and Therapeutics, vol. 15, no. 6, pp. 865–873, 2001. View at Publisher · View at Google Scholar · View at Scopus
  16. H. Ichikawa, Y. Naito, T. Takagi, N. Tomatsuri, N. Yoshida, and T. Yoshikawa, “A specific peroxisome proliferator-induced receptor-γ (PPAR-γ) ligand, pioglitazone, ameliorates gastric mucosal damage induced by ischemia and reperfusion in rats,” Redox Report, vol. 7, no. 5, pp. 343–346, 2002. View at Publisher · View at Google Scholar · View at Scopus
  17. P. C. Konturek, T. Brzozowski, J. Kania et al., “Pioglitazone, a specific ligand of the peroxisome proliferator-activated receptor gamma reduces gastric mucosal injury induced by ischaemia/reperfusion in rat,” Scandinavian Journal of Gastroenterology, vol. 38, no. 5, pp. 468–476, 2003. View at Publisher · View at Google Scholar · View at Scopus
  18. A. Nakajima, K. Wada, H. Miki et al., “Endogenous PPARγ mediates anti-inflammatory activity in murine ischemia-reperfusion injury,” Gastroenterology, vol. 120, no. 2, pp. 460–469, 2001. View at Google Scholar · View at Scopus
  19. T. Takagi, Y. Naito, H. Ichikawa et al., “A PPAR-γ ligand, 15-deoxy-Δ12,14-prostaglandin J2, inhibited gastric mucosal injury induced by ischemia-reperfusion in rats,” Redox Report, vol. 9, no. 6, pp. 376–381, 2004. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  20. I. Villegas, A. R. Martin, W. Toma, and C. A. De La Lastra, “Rosiglitazone, an agonist of peroxisome proliferator-activated receptor gamma, protects against gastric ischemia-reperfusion damage in rats: role of oxygen free radicals generation,” European Journal of Pharmacology, vol. 505, no. 1–3, pp. 195–203, 2004. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  21. K. Wada, A. Nakajima, H. Takahashi et al., “Protective effect of endogenous PPARγ against acute gastric mucosal lesions associated with ischemia-reperfusion,” American Journal of Physiology, vol. 287, no. 2, pp. G452–G458, 2004. View at Publisher · View at Google Scholar · View at PubMed · View at Scopus
  22. S. Lahiri, T. Sen, and G. Palit, “Involvement of glucocorticoid receptor and peroxisome proliferator activated receptor-γ in pioglitazone mediated chronic gastric ulcer healing in rats,” European Journal of Pharmacology, vol. 609, no. 1–3, pp. 118–125, 2009. View at Publisher · View at Google Scholar · View at PubMed
  23. P. C. Konturek, T. Brzozowski, J. Kania et al., “Pioglitazone, a specific ligand of peroxisome proliferator-activated receptor-gamma, accelerates gastric ulcer healing in rat,” European Journal of Pharmacology, vol. 472, no. 3, pp. 213–220, 2003. View at Publisher · View at Google Scholar
  24. T. Brzozowski, P. C. Konturek, R. Pajdo et al., “Agonist of peroxisome proliferator-activated receptor gamma (PPAR-γ): a new compound with potent gastroprotective and ulcer healing properties,” Inflammopharmacology, vol. 13, no. 1–3, pp. 317–330, 2005. View at Publisher · View at Google Scholar · View at PubMed
  25. Y. Naito, T. Takagi, K. Uchiyama et al., “Suppression of intestinal ischemia-reperfusion injury by a specific peroxisome proliferator-activated receptor-γ ligand, pioglitazone, in rats,” Redox Report, vol. 7, no. 5, pp. 294–299, 2002. View at Publisher · View at Google Scholar
  26. S. Cuzzocrea, B. Pisano, L. Dugo et al., “Rosiglitazone and 15-deoxy-Δ12,14-prostaglandin J 2, ligands of the peroxisome proliferator-activated receptor-γ (PPAR-γ), reduce ischaemia/reperfusion injury of the gut,” British Journal of Pharmacology, vol. 140, no. 2, pp. 366–376, 2003. View at Publisher · View at Google Scholar · View at PubMed
  27. C. G. Su, X. Wen, S. T. Bailey et al., “A novel therapy for colitis utilizing PPAR-γ ligands to inhibit the epithelial inflammatory response,” Journal of Clinical Investigation, vol. 104, no. 4, pp. 383–389, 1999. View at Google Scholar
  28. L. J. Saubermann, A. Nakajima, K. Wada et al., “Peroxisome proliferator-activated receptor gamma agonist ligands stimulate a Th2 cytokine response and prevent acute colitis,” Inflammatory Bowel Diseases, vol. 8, no. 5, pp. 330–339, 2002. View at Google Scholar
  29. T. Takagi, Y. Naito, N. Tomatsuri et al., “Pioglitazone, a PPAR-γ ligand, provides protection from dextran sulfate sodium-induced colitis in mice in association with inhibition of the NF-κB-cytokine cascade,” Redox Report, vol. 7, no. 5, pp. 283–289, 2002. View at Publisher · View at Google Scholar
  30. K. L. Schaefer, S. Denevich, C. Ma et al., “Intestinal antiinflammatory effects of thiazolidenedione peroxisome proliferator-activated receptor-γ ligands on T helper type 1 chemokine regulation include nontranscriptional control mechanisms,” Inflammatory Bowel Diseases, vol. 11, no. 3, pp. 244–252, 2005. View at Publisher · View at Google Scholar
  31. J. Bassaganya-Riera, K. Reynolds, S. Martino-Catt et al., “Activation of PPAR γ and δ by conjugated linoleic acid mediates protection from experimental inflammatory bowel disease,” Gastroenterology, vol. 127, no. 3, pp. 777–791, 2004. View at Publisher · View at Google Scholar
  32. P. Desreumaux, L. Dubuquoy, S. Nutten et al., “Attenuation of colon inflammation through activators of the retinoid X receptor (RXR)/peroxisome proliferator-activated receptor γ (PPARγ) heterodimer: a basis for new therapeutic strategies,” Journal of Experimental Medicine, vol. 193, no. 7, pp. 827–838, 2001. View at Publisher · View at Google Scholar
  33. M. Sánchez-Hidalgo, A. R. Martín, I. Villegas, and C. Alarcón de la Lastra, “Rosiglitazone, a PPARγ ligand, modulates signal transduction pathways during the development of acute TNBS-induced colitis in rats,” European Journal of Pharmacology, vol. 562, no. 3, pp. 247–258, 2007. View at Publisher · View at Google Scholar · View at PubMed
  34. C. Rousseaux, B. Lefebvre, L. Dubuquoy et al., “Intestinal antiinflammatory effect of 5-aminosalicylic acid is dependent on peroxisome proliferator-activated receptor-γ,” Journal of Experimental Medicine, vol. 201, no. 8, pp. 1205–1215, 2005. View at Publisher · View at Google Scholar · View at PubMed
  35. C. Lytle, T. J. Tod, K. T. Vo, J. W. Lee, R. D. Atkinson, and D. S. Straus, “The peroxisome proliferator-activated receptor γ ligand rosiglitazone delays the onset of inflammatory bowel disease in mice with interleukin 10 deficiency,” Inflammatory Bowel Diseases, vol. 11, no. 3, pp. 231–243, 2005. View at Publisher · View at Google Scholar
  36. K. Sugawara, T. S. Olson, C. A. Moskaluk et al., “Linkage to peroxisome proliferator-activated receptor-γ in SAMP1/YitFc mice and in human Crohn's disease,” Gastroenterology, vol. 128, no. 2, pp. 351–360, 2005. View at Publisher · View at Google Scholar
  37. B. J. Marshall and J. R. Warren, “Unidentified curved bacilli in the stomach of patients with gastritis and peptic ulceration,” Lancet, vol. 1, no. 8390, pp. 1311–1314, 1984. View at Google Scholar
  38. International Agency for Research on Cancer WHO, “Schistosomes, liver flukes and Helicobacter pylori. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans,” IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, vol. 61, pp. 1–241, 1994. View at Google Scholar
  39. B. L. Slomiany and A. Slomiany, “Suppression of gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide by peroxisome proliferator-activated receptor γ activation,” IUBMB Life, vol. 53, no. 6, pp. 303–308, 2002. View at Publisher · View at Google Scholar · View at PubMed
  40. H. Haruna, T. Shimizu, Y. Ohtsuka et al., “Expression of COX-1, COX-2, and PPAR-γ in the gastric mucosa of children with Helicobacter pylori infection,” Pediatrics International, vol. 50, no. 1, pp. 1–6, 2008. View at Publisher · View at Google Scholar · View at PubMed
  41. P. C. Konturek, J. Kania, V. Kukharsky et al., “Implication of peroxisome proliferator-activated receptor γ and proinflammatory cytokines in gastric carcinogenesis: link to Helicobacter pylori-infection,” Journal of Pharmacological Sciences, vol. 96, no. 2, pp. 134–143, 2004. View at Publisher · View at Google Scholar
  42. C. W. Cheon, D. H. Kim, D. H. Kim, Y. H. Cho, and J. H. Kim, “Effects of ciglitazone and troglitazone on the proliferation of human stomach cancer cells,” World Journal of Gastroenterology, vol. 15, no. 3, pp. 310–320, 2009. View at Publisher · View at Google Scholar
  43. J. Lu, K. Imamura, S. Nomura et al., “Chemopreventive effect of peroxisome proliferator-activated receptor γ on gastric carcinogenesis in mice,” Cancer Research, vol. 65, no. 11, pp. 4769–4774, 2005. View at Publisher · View at Google Scholar · View at PubMed
  44. M. Nagamine, T. Okumura, S. Tanno et al., “PPARγ ligand-induced apoptosis through a p53-dependent mechanism in human gastric cancer cells,” Cancer Science, vol. 94, no. 4, pp. 338–343, 2003. View at Publisher · View at Google Scholar
  45. S. S. Deeb, L. Fajas, M. Nemoto et al., “A Pro12Ala substitution in PPARγ2 associated with decreased receptor activity, lower body mass index and improved insulin sensitivity,” Nature Genetics, vol. 20, no. 3, pp. 284–287, 1998. View at Publisher · View at Google Scholar · View at PubMed
  46. S. Landi, V. Moreno, L. Gioia-Patricola et al., “Association of common polymorphisms in inflammatory genes interleukin (IL)6, IL8, tumor necrosis factor α, NFKB1, and peroxisome proliferator-activated receptor γ with colorectal cancer,” Cancer Research, vol. 63, no. 13, pp. 3560–3566, 2003. View at Google Scholar
  47. D. Altshuler, J. N. Hirschhorn, M. Klannemark et al., “The common PPARγ Pro12Ala polymorphism is associated with decreased risk of type 2 diabetes,” Nature Genetics, vol. 26, no. 1, pp. 76–80, 2000. View at Publisher · View at Google Scholar · View at PubMed
  48. S. J. Chae, J. J. Kim, Y. M. Choi, J. M. Kim, Y. M. Cho, and S. Y. Moon, “Peroxisome proliferator-activated receptor-γ and its coactivator-1α gene polymorphisms in korean women with polycystic ovary syndrome,” Gynecologic and Obstetric Investigation, vol. 70, no. 1, pp. 1–7, 2010. View at Publisher · View at Google Scholar · View at PubMed
  49. S.-H. Oh, S.-M. Park, J.-S. Park et al., “Association analysis of peroxisome proliferator-activated receptors gamma gene polymorphisms with asprin hypersensitivity in asthmatics,” Allergy, Asthma and Immunology Research, vol. 1, no. 1, pp. 30–35, 2009. View at Publisher · View at Google Scholar · View at PubMed
  50. K. R. Hwang, Y. M. Choi, J. M. Kim et al., “Association of peroxisome proliferator-activated receptor-γ 2 Pro12Ala polymorphism with advanced-stage endometriosis,” American Journal of Reproductive Immunology. In press.
  51. S.-Y. Liao, Z.-R. Zeng, W. K. Leung et al., “Peroxisome proliferator-activated receptor-gamma Pro12Ala polymorphism, Helicobacter pylori infection and non-cardia gastric carcinoma in Chinese,” Alimentary Pharmacology and Therapeutics, vol. 23, no. 2, pp. 289–294, 2006. View at Publisher · View at Google Scholar · View at PubMed
  52. K. N. Prasad, A. Saxena, U. C. Ghoshal, M. R. Bhagat, and N. Krishnani, “Analysis of Pro12Ala PPAR gamma polymorphism and Helicobacter pylori infection in gastric adenocarcinoma and peptic ulcer disease,” Annals of Oncology, vol. 19, no. 7, pp. 1299–1303, 2008. View at Publisher · View at Google Scholar · View at PubMed
  53. T. Tahara, T. Arisawa, T. Shibata et al., “Influence of peroxisome proliferator-activated receptor (PPAR)γ Plo12Ala polymorphism as a shared risk marker for both gastric cancer and impaired fasting glucose (IFG) in Japanese,” Digestive Diseases and Sciences, vol. 53, no. 3, pp. 614–621, 2008. View at Publisher · View at Google Scholar · View at PubMed
  54. L. Dubuquoy, E. A. Jansson, S. Deeb et al., “Impaired expression of peroxisome proliferator-activated receptor γin ulcerative colitis,” Gastroenterology, vol. 124, no. 5, pp. 1265–1276, 2003. View at Publisher · View at Google Scholar
  55. S. E. Chang, S. H. Dong, H. L. Seung et al., “Attenuation of colonic inflammation by PPARγ in intestinal epithelial cells: effect on toll-like receptor pathway,” Digestive Diseases and Sciences, vol. 51, no. 4, pp. 693–697, 2006. View at Publisher · View at Google Scholar · View at PubMed
  56. N. Baregamian, J. M. Mourot, A. R. Ballard, B. M. Evers, and D. H. Chung, “PPAR-γ agonist protects against intestinal injury during necrotizing enterocolitis,” Biochemical and Biophysical Research Communications, vol. 379, no. 2, pp. 423–427, 2009. View at Publisher · View at Google Scholar · View at PubMed
  57. R. J. Xavier and D. K. Podolsky, “Unravelling the pathogenesis of inflammatory bowel disease,” Nature, vol. 448, no. 7152, pp. 427–434, 2007. View at Publisher · View at Google Scholar · View at PubMed
  58. K. Katayama, K. Wada, A. Nakajima et al., “A novel PPARγ gene therapy to control inflammation associated with inflammatory bowel disease in a murine model,” Gastroenterology, vol. 124, no. 5, pp. 1315–1324, 2003. View at Publisher · View at Google Scholar
  59. L. Klotz, I. Dani, F. Edenhofer et al., “Peroxisome proliferator-activated receptor γ control of dendritic cell function contributes to development of CD4+ T cell anergy,” Journal of Immunology, vol. 178, no. 4, pp. 2122–2131, 2007. View at Google Scholar
  60. R. Hontecillas and J. Bassaganya-Riera, “Peroxisome proliferator-activated receptor γ is required for regulatory CD4+ T cell-mediated protection against colitis,” Journal of Immunology, vol. 178, no. 5, pp. 2940–2949, 2007. View at Google Scholar
  61. J. D. Lewis, G. R. Lichtenstein, R. B. Stein et al., “An open-label trial of the PPARγ ligand rosiglitazone for active ulcerative colitis,” American Journal of Gastroenterology, vol. 96, no. 12, pp. 3323–3328, 2001. View at Publisher · View at Google Scholar
  62. R. N. DuBois, R. Gupta, J. Brockman, B. S. Reddy, S. L. Krakow, and M. A. Lazar, “The nuclear eicosanoid receptor, PPARγ, is aberrantly expressed in colonic cancers,” Carcinogenesis, vol. 19, no. 1, pp. 49–53, 1998. View at Publisher · View at Google Scholar
  63. P. Sarraf, E. Mueller, D. Jones et al., “Differentiation and reversal of malignant changes in colon cancer through PPARγ,” Nature Medicine, vol. 4, no. 9, pp. 1046–1052, 1998. View at Publisher · View at Google Scholar · View at PubMed
  64. W.-L. Yang and H. Frucht, “Activation of the PPAR pathway induces apoptosis and COX-2 inhibition in HT-29 human colon cancer cells,” Carcinogenesis, vol. 22, no. 9, pp. 1379–1383, 2001. View at Google Scholar
  65. E. Osawa, A. Nakajima, K. Wada et al., “Peroxisome proliferator-activated receptor γ ligands suppress colon carcinogenesis induced by azoxymethane in mice,” Gastroenterology, vol. 124, no. 2, pp. 361–367, 2003. View at Publisher · View at Google Scholar · View at PubMed
  66. A.-M. Lefebvre, I. Chen, P. Desreumaux et al., “Activation of the peroxisome proliferator-activated receptor γ promotes the development of colon tumors in C57BL/6J-APC(Min)/+ mice,” Nature Medicine, vol. 4, no. 9, pp. 1053–1057, 1998. View at Publisher · View at Google Scholar · View at PubMed