Peroxisome proliferator-activated receptor gamma is induced during differentiation of colon epithelium cells

Are single nucleotide polymorphisms underutilized for guiding treatment of inflammatory bowel disease?

Inflammatory bowel disease (IBD), encompassing Crohn's disease (CD), ulcerative colitis (UC) and IBD unclassified (IBDU), significantly impacts quality of life. Despite significant advances in the management of the conditions, responses to treatments vary greatly, and this is due partly to our natural genetic variation. Here we will review the evidence for whether single nucleotide polymorphisms (SNPs) have the potential to guide treatment decisions for people with IBD. We will first consider SNPs that exhibit strong associations with IBD pathogenesis and their relevance to epithelial barrier integrity, cytokine production, and immune system function. Then, we will cover those SNPs implicated in altering response to our various current IBD therapeutics, including the recently implemented drugs ustekinumab and tofacitinib. Finally, we will explore lesser-known SNPs that exhibit complex relationships with the disease and which may be undervalued as pharmacogenetic tools. Overall, it will be demonstrated that SNPs associated with IBD pathology are largely distinct from those predicting response to treatments and that new discoveries of clinically useful tools can be expected from therapy-focused investigations. Given the growing list of treatments available, we argue that beneficial personalization of treatments based on SNPs is still underutilized.

Oroxyloside protects against dextran sulfate sodium-induced colitis by inhibiting ER stress via PPARγ activation

Ulcerative colitis (UC), a prevalent form of inflammatory bowel disease (IBD), may result from immune system dysfunction, leading to the sustained overproduction of reactive oxygen species (ROS) and subsequent cellular oxidative stress damage. Recent studies have identified both peroxisome proliferator-activated receptor-γ (PPARγ) and endoplasmic reticulum (ER) stress as critical targets for the treatment of IBD. Oroxyloside (C22H20O11), derived from the root of Scutellariabaicalensis Georgi, has traditionally been used in treating inflammatory diseases. In this study, we investigated the molecular mechanisms by which oroxyloside mitigates dextran sulfate sodium (DSS)-induced colitis. We examined the effects of oroxyloside on ROS-mediated ER stress in colitis, including the protein expressions of GRP78, p-PERK, p-eIF2α, ATF4, and CHOP, which are associated with ER stress. The beneficial impact of oroxyloside was reversed by the PPARγ antagonist GW9662 (1 mg·kg-1, i.v.) in vivo. Furthermore, oroxyloside decreased pro-inflammatory cytokines and ROS production in both bone marrow-derived macrophages (BMDM) and the mouse macrophage cell line RAW 264.7. However, PPARγ siRNA transfection blocked the anti-inflammatory effect of oroxyloside and even abolished ROS generation and ER stress activation inhibited by oroxyloside in vitro. In conclusion, our study demonstrates that oroxyloside ameliorates DSS-induced colitis by inhibiting ER stress via PPARγ activation, suggesting that oroxyloside might be a promising effective agent for IBD.

Metabolic Interaction Between Host and the Gut Microbiota During High-Fat Diet-Induced Colorectal Cancer

Colorectal cancer (CRC) is the second-highest cause of cancer-associated mortality among both men and women worldwide. One of the risk factors for CRC is obesity, which is correlated with a high-fat diet prevalent in Western dietary habits. The association between an obesogenic high-fat diet and CRC has been established for several decades; however, the mechanisms by which a high-fat diet increases the risk of CRC remain unclear. Recent studies indicate that gut microbiota strongly influence the pathogenesis of both high-fat diet-induced obesity and CRC. The gut microbiota is composed of hundreds of bacterial species, some of which are implicated in CRC. In particular, the expansion of facultative anaerobic Enterobacteriaceae, which is considered a microbial signature of intestinal microbiota functional imbalance (dysbiosis), is associated with both high-fat diet-induced obesity and CRC. Here, we review the interaction between the gut microbiome and its metabolic byproducts in the context of colorectal cancer (CRC) during high-fat diet-induced obesity. In addition, we will cover how a high-fat diet can drive the expansion of genotoxin-producing Escherichia coli by altering intestinal epithelial cell metabolism during gut inflammation conditions.

Gut dysbiosis: Ecological causes and causative effects on human disease

The gut microbiota plays a role in many human diseases, but high-throughput sequence analysis does not provide a straightforward path for defining healthy microbial communities. Therefore, understanding mechanisms that drive compositional changes during disease (gut dysbiosis) continues to be a central goal in microbiome research. Insights from the microbial pathogenesis field show that an ecological cause for gut dysbiosis is an increased availability of host-derived respiratory electron acceptors, which are dominant drivers of microbial community composition. Similar changes in the host environment also drive gut dysbiosis in several chronic human illnesses, and a better understanding of the underlying mechanisms informs approaches to causatively link compositional changes in the gut microbiota to an exacerbation of symptoms. The emerging picture suggests that homeostasis is maintained by host functions that control the availability of resources governing microbial growth. Defining dysbiosis as a weakening of these host functions directs attention to the underlying cause and identifies potential targets for therapeutic intervention.

Microbial Metabolite Dysbiosis and Colorectal Cancer

The global burden of colorectal cancer (CRC) is expected to continuously increase. Through research performed in the past decades, the effects of various environmental factors on CRC development have been well identified. Diet, the gut microbiota and their metabolites are key environmental factors that profoundly affect CRC development. Major microbial metabolites with a relevance for CRC prevention and pathogenesis include dietary fiber-derived short-chain fatty acids, bile acid derivatives, indole metabolites, polyamines, trimethylamine-N-oxide, formate, and hydrogen sulfide. These metabolites regulate various cell types in the intestine, leading to an altered intestinal barrier, immunity, chronic inflammation, and tumorigenesis. The physical, chemical, and metabolic properties of these metabolites along with their distinct functions to trigger host receptors appear to largely determine their effects in regulating CRC development. In this review, we will discuss the current advances in our understanding of the major CRC-regulating microbial metabolites, focusing on their production and interactive effects on immune responses and tumorigenesis in the colon.

Tutorial: Microbiome studies in drug metabolism

The human gastrointestinal tract is home to a dense population of microorganisms whose metabolism impacts human health and physiology. The gut microbiome encodes millions of genes, the products of which endow our bodies with unique biochemical activities. In the context of drug metabolism, microbial biochemistry in the gut influences humans in two major ways: (1) by producing small molecules that modulate expression and activity of human phase I and II pathways; and (2) by directly modifying drugs administered to humans to yield active, inactive, or toxic metabolites. Although the capacity of the microbiome to modulate drug metabolism has long been known, recent studies have explored these interactions on a much broader scale and have revealed an unprecedented scope of microbial drug metabolism. The implication of this work is that we might be able to predict the capacity of an individual's microbiome to metabolize drugs and use this information to avoid toxicity and inform proper dosing. Here, we provide a tutorial of how to study the microbiome in the context of drug metabolism, focusing on in vitro, rodent, and human studies. We then highlight some limitations and opportunities for the field.

Emodin targeting the colonic metabolism via PPARγ alleviates UC by inhibiting facultative anaerobe

BACKGROUND

Emodin is an active ingredient of traditional Chinese medicine Rheum palmatum L. and Polygonum cuspidatum, which possesses anti-inflammatory and intestinal mucosal protection effects. Our previous study found that emodin significantly alleviated ulcerative colitis induced by sodium dextran sulfate (DSS). In this study, we found the underlying mechanism of emodin on ulcerative colitis (UC).

PURPOSE

We aimed to further explore the mechanism of emodin in the treatment of ulcerative colitis from the perspective of metabolism and intestinal flora.

METHODS

Ulcerative colitis was induced by 3% sodium dextran sulfate (DSS) on mice, and the mice were respectively treated with mesalazine, rosiglitazone, emodin, and emodin combined with GW9662 (PPARγ inhibitor) simultaneously. Weight changes, the disease activity index (DAI), colonic length, and pathologic changes in colon were used to evaluate the efficacy of emodin. LC-MS/MS was performed for metabolomics analysis of colon. In addition, intestinal flora was assessed using 16S rDNA sequencing. A vector-based short hairpin RNA (shRNA) method was used to silence PPARγ gene expression in Caco-2 cells.

RESULTS

Emodin binds to the active site of PPARγ protein and forms hydrogen bond interaction with ARG288 and CYS285 amino acids. Furthermore, Emodin significantly promotes the protein expression of PPARγ, while inhibiting iNOS and NF-kB p65 in UC mice, however, this effect is hardly shown when it is combined with GW9662 (the inhibitor of PPARγ). Meanwhile, emodin suppresses the expression of iNOS in Caco-2 cells induced with IFNγ and IL-22, but has no effect on its expression in shPPARγ-Caco-2 cells. In addition, through activating PPARγ signal pathway, emodin is capable of regulating colonic metabolism including oxidative phosphorylation and citrulline metabolism and effecting luminal availability of oxygen and nitrate. This promotes the recovery of anoxic environment of colon epithelial cells, which strains the growth and expansion of Enterobacteriaceae.

CONCLUSION

The mechanism of Emodin in the treatment of ulcerative colitis relies on its regulation of PPARγ signal pathway, which could modulate colonic metabolism and restore intestinal homeostasis.

Mitochondrial function in intestinal epithelium homeostasis and modulation in diet-induced obesity

Background

Systemic low-grade inflammation observed in diet-induced obesity has been associated with dysbiosis and disturbance of intestinal homeostasis. This latter relies on an efficient epithelial barrier and coordinated intestinal epithelial cell (IEC) renewal that are supported by their mitochondrial function. However, IEC mitochondrial function might be impaired by high fat diet (HFD) consumption, notably through gut-derived metabolite production and fatty acids, that may act as metabolic perturbators of IEC.

Scope of review

This review presents the current general knowledge on mitochondria, before focusing on IEC mitochondrial function and its role in the control of intestinal homeostasis, and featuring the known effects of nutrients and metabolites, originating from the diet or gut bacterial metabolism, on IEC mitochondrial function. It then summarizes the impact of HFD on mitochondrial function in IEC of both small intestine and colon and discusses the possible link between mitochondrial dysfunction and altered intestinal homeostasis in diet-induced obesity.

Major conclusions

HFD consumption provokes a metabolic shift toward fatty acid β-oxidation in the small intestine epithelial cells and impairs colonocyte mitochondrial function, possibly through downstream consequences of excessive fatty acid β-oxidation and/or the presence of deleterious metabolites produced by the gut microbiota. Decreased levels of ATP and concomitant O₂ leaks into the intestinal lumen could explain the alterations of intestinal epithelium dynamics, barrier disruption and dysbiosis that contribute to the loss of epithelial homeostasis in diet-induced obesity. However, the effect of HFD on IEC mitochondrial function in the small intestine remains unknown and the precise mechanisms by which HFD induces mitochondrial dysfunction in the colon have not been elucidated so far.

α-Bisabolol Mitigates Colon Inflammation by Stimulating Colon PPAR-γ Transcription Factor: In Vivo and In Vitro Study

The incidence and prevalence of inflammatory bowel disease (IBD, Crohn’s disease, and ulcerative colitis) are increasing worldwide. The etiology of IBD is multifactorial, including genetic predisposition, dysregulated immune response, microbial dysbiosis, and environmental factors. However, many of the existing therapies are associated with marked side effects. Therefore, the development of new drugs for IBD treatment is an important area of investigation. Here, we investigated the anti-inflammatory effects of α-bisabolol, a naturally occurring monocyclic sesquiterpene alcohol present in many aromatic plants, in colonic inflammation. To address this, we used molecular docking and dynamic studies to understand how α-bisabolol interacts with PPAR-γ, which is highly expressed in the colonic epithelium: in vivo (mice) and in vitro (RAW264.7 macrophages and HT-29 colonic adenocarcinoma cells) models. The molecular docking and dynamic analysis revealed that α-bisabolol interacts with PPAR-γ, a nuclear receptor protein that is highly expressed in the colon epithelium. Treatment with α-bisabolol in DSS-administered mice significantly reduced Disease Activity Index (DAI), myeloperoxidase (MPO) activity, and colonic length and protected the microarchitecture of the colon. α-Bisabolol treatment also reduced the expression of proinflammatory cytokines (IL-6, IL1β, TNF-α, and IL-17A) at the protein and mRNA levels. The expression of COX-2 and iNOS inflammatory mediators were reduced along with tissue nitrite levels. Furthermore, α-bisabolol decreased the phosphorylation of activated mitogen-activated protein kinase (MAPK) signaling and nuclear factor kappa B (NFκB) proteins and enhanced colon epithelial PPAR-γ transcription factor expression. However, the PPAR-α and β/δ expression was not altered, indicating α-bisabolol is a specific stimulator of PPAR-γ. α-Bisabolol also increased the PPAR-γ transcription factor expression but not PPAR-α and β/δ in pretreated in LPS-stimulated RAW264.7 macrophages. α-Bisabolol significantly decreased the expression of proinflammatory chemokines (CXCL-1 and IL-8) mRNA in HT-29 cells treated with TNF-α and HT-29 PPAR-γ promoter activity. These results demonstrate that α-bisabolol mitigates colonic inflammation by inhibiting MAPK signaling and stimulating PPAR-γ expression.

The AT1 Receptor Blocker Telmisartan Reduces Intestinal Mucus Thickness in Obese Mice

The angiotensin II (type 1) (AT₁) receptor blocker telmisartan (TEL) is beneficial for the treatment of individuals suffering from metabolic syndrome. As we have shown that TEL has an impact on gut microbiota, we investigated here whether TEL influences gut barrier function. C57BL/6N mice were fed with chow or high-fat diet (HFD) and treated with vehicle or TEL (8 mg/kg/day). Mucus thickness was determined by immunohistochemistry. Periodic Acid-Schiff staining allowed the number of goblet cells to be counted. Using western blots, qPCR, and immunohistochemistry, factors related to mucus biosynthesis (Muc2, St6galnac), proliferation (Ki-67), or necroptosis (Rip3) were measured. The influence on cell viability was determined in vitro by using losartan, as the water solubility of TEL was too low for in vitro experiments. Upon HFD, mice developed obesity as well as leptin and insulin resistance, which were prevented by TEL. Mucus thickness upon HFD-feeding was diminished. Independent of feeding, TEL additionally reduced mucus thickness. Numbers of goblet cells were not affected by HFD-feeding and TEL. St6galnac expression was increased by TEL. Rip3 was increased in TEL-treated and HFD-fed mice, while Ki-67 decreased. Cell viability was diminished by using >1 mM losartan. The anti-obese effect of TEL was associated with a decrease in mucus thickness, which was likely not related to a lower expression of Muc2 and goblet cells. A decrease in Ki-67 and increase in Rip3 indicates lower cell proliferation and increased necroptosis upon TEL. However, direct cell toxic effects are ruled out, as in vivo concentrations are lower than 1 mM.

Effects of Oral Glucose-Lowering Agents on Gut Microbiota and Microbial Metabolites

The current research and existing facts indicate that type 2 diabetes mellitus (T2DM) is characterized by gut microbiota dysbiosis and disturbed microbial metabolites. Oral glucose-lowering drugs are reported with pleiotropic beneficial effects, including not only a decrease in glucose level but also weight loss, antihypertension, anti-inflammation, and cardiovascular protection, but the underlying mechanisms are still not clear. Evidence can be found showing that oral glucose-lowering drugs might modify the gut microbiome and thereby alter gastrointestinal metabolites to improve host health. Although the connections among gut microbial communities, microbial metabolites, and T2DM are complex, figuring out how antidiabetic agents shape the gut microbiome is vital for optimizing the treatment, meaningful for the instruction for probiotic therapy and gut microbiota transplantation in T2DM. In this review, we focused on the literatures in gut microbiota and its metabolite profile alterations beneficial from oral antidiabetic drugs, trying to provide implications for future study in the developing field of these drugs, such as combination therapies, pre- and probiotics intervention in T2DM, and subjects with pregestational diabetes and gestational diabetes mellitus.

Revisiting the steps of Salmonella gut infection with a focus on antagonistic interbacterial interactions

A commensal microbial community is established in the mammalian gut during its development, and these organisms protect the host against pathogenic invaders. The hallmark of noninvasive Salmonella gut infection is the induction of inflammation via effector proteins secreted by the type III secretion system, which modulate host responses to create a new niche in which the pathogen can overcome the colonization resistance imposed by the microbiota. Several studies have shown that endogenous microbes are important to control Salmonella infection by competing for resources. However, there is limited information about antimicrobial mechanisms used by commensals and pathogens during these in vivo disputes for niche control. This review aims to revisit the steps that Salmonella needs to overcome during gut colonization-before and after the induction of inflammation-to achieve an effective infection. We focus on a series of reported and hypothetical antagonistic interbacterial interactions in which both contact-independent and contact-dependent mechanisms might define the outcome of the infection.

Crosstalk Between Intestinal Microbiota Derived Metabolites and Tissues in Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an evidence based- cellular immunotherapy for hematological malignancies. Immune reactions not only promote graft-versus-tumor effects that kill hematological malignant cells but also graft-versus-host disease (GVHD) that is the primary complication characterized by systemic organ damages consisting of T-cells and antigen presenting cells (APCs) activation. GVHD has long been recognized as an immunological reaction that requires an immunosuppressive treatment targeting immune cells. However immune suppression cannot always prevent GVHD or effectively treat it once it has developed. Recent studies using high-throughput sequencing technology investigated the impact of microbial flora on GVHD and provided profound insights of the mechanism of GVHD other than immune cells. Allo-HSCT affects the intestinal microbiota and microbiome-metabolome axis that can alter intestinal homeostasis and the severity of experimental GVHD. This axis can potentially be manipulated via dietary intervention or metabolites produced by intestinal bacteria affected post-allo-HSCT. In this review, we discuss the mechanism of experimental GVHD regulation by the complex microbial community-metabolites-host tissue axis. Furthermore, we summarize the major findings of microbiome-based immunotherapeutic approaches that protect tissues from experimental GVHD. Understanding the complex relationships between gut microbiota-metabolites-host tissues axis provides crucial insight into the pathogenesis of GVHD and advances the development of new therapeutic approaches.

Naringin Exerts Therapeutic Effects on Mice Colitis: A Study Based on Transcriptomics Combined With Functional Experiments

Naringin has been shown to exert protective effects in an animal model of ulcerative colitis, but detailed mechanisms remain unclear. This study aimed to investigate function and signaling mechanisms underlying naringin-induced therapeutic effects on colitis. Two mouse models were established to mimic human Inflammatory bowel disease (IBD) by treating drinking water with dextran sodium sulphate or intra-colonic administration of 2, 4, 6-trinitrobenzene sulfonic acid. Transcriptomics combined with functional experiments were used to investigate underlying mechanisms. Colitis symptoms, including weight loss and high disease activity index were significantly reversed by naringin. The inflammatory response, oxidative reactions, and epithelial cell apoptosis that occur with colitis were also alleviated by naringin. After naringin treatment, transcriptomics results identified 753 differentially expressed mRNAs that were enriched in signaling pathways, including the neuroactive ligand-receptor interaction, calcium signaling, and peroxisome proliferator-activated receptor (PPAR) signaling. The naringin-induced alleviation of colitis was significantly inhibited by the PPAR-γ inhibitor BADGE. In IEC-6 and RAW264.7 cells incubated with lipopolysaccharide (LPS), NF-κB-p65, a downstream protein of PPAR-γ, was significantly increased. Naringin suppressed LPS-induced high expression of NF-κB-p65, which was inhibited by small interfering RNA targeting PPAR-γ. Our study clarifies detailed mechanisms underlying naringin-induced therapeutic effects on mice colitis, and PPAR-γ was found to be the main target of naringin by functional experiments both in vivo and in vitro. Our study supplies new scientific information for the use of naringin in colitis treatment.

Gut microbiota-derived metabolites as key mucosal barrier modulators in obesity

A significant breakthrough in the field of obesity research was the demonstration that an obese phenotype could be manipulated by modulating the gut microbiota. An important next step is to elucidate a human-relevant “map’’ of microbiota-host interactions that regulate the metabolic health of the host. An improved understanding of this crosstalk is a prerequisite for optimizing therapeutic strategies to combat obesity. Intestinal mucosal barrier dysfunction is an important contributor to metabolic diseases and has also been found to be involved in a variety of other chronic inflammatory conditions, including cancer, neurodegeneration, and aging. The mechanistic basis for intestinal barrier dysfunction accompanying metabolic disorders remains poorly understood. Understanding the molecular and cellular modulators of intestinal barrier function will help devise improved strategies to counteract the detrimental systemic consequences of gut barrier breakage. Changes in the composition and function of the gut microbiota, i.e., dysbiosis, are thought to drive obesity-related pathogenesis and may be one of the most important drivers of mucosal barrier dysfunction. Many effects of the microbiota on the host are mediated by microbiota-derived metabolites. In this review, we focus on several relatively well-studied microbial metabolites that can influence intestinal mucosal homeostasis and discuss how they might affect metabolic diseases. The design and use of microbes and their metabolites that are locally active in the gut without systemic side effects are promising novel and safe therapeutic modalities for metabolic diseases.

Gut microbiota-derived inosine from dietary barley leaf supplementation attenuates colitis through PPARγ signaling activation

BACKGROUND

Ulcerative colitis is a type of chronic inflammatory bowel disease closely associated with gut microbiota dysbiosis and intestinal homeostasis dysregulation. Barley leaf (BL) has a long history of use in Traditional Chinese Medicine with potential health-promoting effects on intestinal functions. However, its mechanism of action is not yet clear. Here, we explore the potential modulating roles of gut microbial metabolites of BL to protect against colitis and elucidate the underlying molecular mechanisms.

RESULTS

Using 16S rRNA gene-based microbiota analysis, we first found that dietary supplementation of BL ameliorated dextran sulfate sodium (DSS)-induced gut microbiota dysbiosis. The mechanisms by which BL protected against DSS-induced colitis were resulted from improved intestinal mucosal barrier functions via the activation of peroxisome proliferator-activated receptor (PPAR)γ signaling. In addition, metabolomic profiling analysis showed that the gut microbiota modulated BL-induced metabolic reprograming in the colonic tissues particularly by the enhancement of glycolysis process. Notably, dietary BL supplementation resulted in the enrichment of microbiota-derived purine metabolite inosine, which could activate PPARγ signaling in human colon epithelial cells. Furthermore, exogenous treatment of inosine reproduced similar protective effects as BL to protect against DSS-induced colitis through improving adenosine 2A receptor (A_2AR)/PPARγ-dependent mucosal barrier functions.

CONCLUSIONS

Overall, our findings suggest that the gut microbiota-inosine-A_2AR/PPARγ axis plays an important role in the maintenance of intestinal homeostasis, which may represent a novel approach for colitis prevention via manipulation of the gut microbial purine metabolite. Video Abstract.

Posttranslational modifications as therapeutic targets for intestinal disorders

A variety of biological processes are regulated by posttranslational modifications. Posttranslational modifications including phosphorylation, ubiquitination, glycosylation, and proteolytic cleavage, control diverse physiological functions in the gastrointestinal tract. Therefore, a better understanding of their implications in intestinal diseases, including inflammatory bowel disease, irritable bowel syndrome, celiac disease, and colorectal cancer would provide a basis for the identification of novel biomarkers as well as attractive therapeutic targets. Posttranslational modifications can be common denominators, as well as distinct biomarkers, characterizing pathological differences of various intestinal diseases. This review provides experimental evidence that identifies changes in posttranslational modifications from patient samples, primary cells, or cell lines in intestinal disorders, and a summary of carefully selected information on the use of pharmacological modulators of protein modifications as therapeutic options.

Characterization of local gut microbiome and intestinal transcriptome responses to rosiglitazone treatment in diabetic db/db mice

The gut microbiota has been implicated in the therapeutic effects of antidiabetics. It is unclear if antidiabetics directly influences gut microbiome-host interaction. Oral peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists, such as rosiglitazone, are potent insulin sensitizers used in the treatment of type 2 diabetes (T2D). PPAR-γ is abundantly expressed in the intestine, making it possible that PPAR-γ agonists directly influences gut microbiome-host homeostasis. The presented study therefore aimed to characterize local gut microbiome and intestinal transcriptome responses in diabetic db/db mice following rosiglitazone treatment. Diabetic B6.BKS(D)-Lepr^db/J (db/db) mice (8 weeks of age) received oral dosing once daily with vehicle (n = 12) or rosiglitazone (3 mg/kg, n = 12) for 8 weeks. Gut segments (duodenum, jejunum, ileum, caecum, and colon) were sampled for paired analysis of gut microbiota and host transcriptome signatures using full-length bacterial 16S rRNA sequencing and RNA sequencing (n = 5-6 per group). Treatment with rosiglitazone improved glucose homeostasis without influencing local gut microbiome composition in db/db mice. In contrast, rosiglitazone promoted marked changes in ileal and colonic gene expression signatures associated with peroxisomal and mitochondrial lipid metabolism, carbohydrate utilization and immune regulation. In conclusion, rosiglitazone treatment markedly affected transcriptional markers of intestinal lipid metabolism and immune regulation but had no effect on the gut microbiome in diabetic db/db mice.

Activation of PPARγ and inhibition of cell proliferation reduces key proteins associated with the basal subtype of bladder cancer in As3+-transformed UROtsa cells

Environmental exposure to arsenite (As³⁺) has a strong association with the development of human urothelial cancer (UC) and is the 5^th most common cancer in men and the 12^th most common cancer in women. Muscle invasive urothelial cancer (MIUC) are grouped into basal or luminal molecular subtypes based on their gene expression profile. The basal subtype is more aggressive and can be associated with squamous differentiation, characterized by high expression of keratins (KRT1, 5, 6, 14, and 16) and epidermal growth factor receptor (EGFR) within the tumors. The luminal subtype is less aggressive and is predominately characterized by elevated gene expression of peroxisome proliferator-activated receptor- gamma (PPARγ) and forkhead box protein A1 (FOXA1). We have previously shown that As³⁺-transformed urothelial cells (As-T) exhibit a basal subtype of UC expressing genes associated with squamous differentiation. We hypothesized that the molecular subtype of the As-T cells could be altered by inducing the expression of PPARγ and/or inhibiting the proliferation of the cells. Non-transformed and As-T cells were treated with Troglitazone (TG, PPARG agonist, 10 μM), PD153035 (PD, an EGFR inhibitor, 1 μM) or a combination of TG and PD for 3 days. The results obtained demonstrate that treatment of the As-T cells with TG upregulated the expression of PPARγ and FOXA1 whereas treatment with PD decreased the expression of some of the basal keratins. However, a combined treatment of TG and PD resulted in a consistent decrease of several proteins associated with the basal subtype of bladder cancers (KRT1, KRT14, KRT16, P63, and TFAP2A). Our data suggests that activation of PPARγ while inhibiting cell proliferation facilitates the regulation of genes involved in maintaining the luminal subtype of UC. In vivo animal studies are needed to address the efficacy of using PPARγ agonists and/or proliferation inhibitors to reduce tumor grade/stage of MIUC.

Gut Epithelial Metabolism as a Key Driver of Intestinal Dysbiosis Associated with Noncommunicable Diseases

In high-income countries, the leading causes of death are noncommunicable diseases (NCDs), such as obesity, cancer, and cardiovascular disease. An important feature of most NCDs is inflammation-induced gut dysbiosis characterized by a shift in the microbial community structure from obligate to facultative anaerobes such as Proteobacteria This microbial imbalance can contribute to disease pathogenesis by either a depletion in or the production of microbiota-derived metabolites. However, little is known about the mechanism by which inflammation-mediated changes in host physiology disrupt the microbial ecosystem in our large intestine leading to disease. Recent work by our group suggests that during gut homeostasis, epithelial hypoxia derived from peroxisome proliferator-activated receptor γ (PPAR-γ)-dependent β-oxidation of microbiota-derived short-chain fatty acids limits oxygen availability in the colon, thereby maintaining a balanced microbial community. During inflammation, disruption in gut anaerobiosis drives expansion of facultative anaerobic Enterobacteriaceae, regardless of their pathogenic potential. Therefore, our research group is currently exploring the concept that dysbiosis-associated expansion of Enterobacteriaceae can be viewed as a microbial signature of epithelial dysfunction and may play a greater role in different models of NCDs, including diet-induced obesity, atherosclerosis, and inflammation-associated colorectal cancer.

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.

Lycopene supplementation regulates the gene expression profile and fat metabolism of breeding hens

This study investigated the effects of lycopene on the gene expression profile and expression of genes related to fat metabolism of Xinghua breeding hens. Seven hundred and twenty healthy breeding hens were randomly assigned to four treatments; each treatment was replicated six times with 30 hens each. Broken rice and soybean meal were adopted for the basal diet and added with 0 (control group), 20, 40 and 80 mg/kg lycopene respectively. Gene expression profile of the liver induced by lycopene and expression of genes related to fat metabolism in hens liver and intestine were analysed after 42-day feeding trial including 7-day pre-feeding period and 35-day formal period. The genes involved in fat metabolism were analysed, and we found that lycopene significantly increased the expression of PGC1α, PPARα, RXRα and RARα in the liver, PPARγ, RXRα and RXRγ in the jejunum, and RARα in the duodenum (p < .05); reduced the expression of FABP1 and FABP10 in the liver, and FATP4 in the jejunum (p < .05). By analysing gene expression profile, 158 differentially expressed genes (DEGs) including 69 up-regulated genes and 89 down-regulated genes were obtained between control group and 40 mg/kg group. KEGG pathway analysis was performed on all DEGs, and 5 pathways were obtained. In conclusion, lycopene can affect the expression of related genes, and this may be one of the reasons that lycopene can regulate fat metabolism.

Increased Epithelial Oxygenation Links Colitis to an Expansion of Tumorigenic Bacteria

Intestinal inflammation is a risk factor for colorectal cancer formation, but the underlying mechanisms remain unknown. Here, we investigated whether colitis alters the colonic microbiota to enhance its cancer-inducing activity. Colitis increased epithelial oxygenation in the colon of mice and drove an expansion of Escherichia coli within the gut-associated microbial community through aerobic respiration. An aerobic expansion of colibactin-producing E. coli was required for the cancer-inducing activity of this pathobiont in a mouse model of colitis-associated colorectal cancer formation. We conclude that increased epithelial oxygenation in the colon is associated with an expansion of a prooncogenic driver species, thereby increasing the cancer-inducing activity of the microbiota.IMPORTANCE One of the environmental factors important for colorectal cancer formation is the gut microbiota, but the habitat filters that control its cancer-inducing activity remain unknown. Here, we show that chemically induced colitis elevates epithelial oxygenation in the colon, thereby driving an expansion of colibactin-producing Escherichia coli, a prooncogenic driver species. These data suggest that elevated epithelial oxygenation is a potential risk factor for colorectal cancer formation because the consequent changes in the gut habitat escalate the cancer-inducing activity of the microbiota.

Metabolism at the centre of the host-microbe relationship

Maintaining homoeostatic host–microbe interactions is vital for host immune function. The gut microbiota shapes the host immune system and the immune system reciprocally shapes and modifies the gut microbiota. However, our understanding of how these microbes are tolerated and how individual, or communities of, gut microbes influence host function is limited. This review will focus on metabolites as key mediators of this complex host–microbe relationship. It will look at the central role of epithelial metabolism in shaping the gut microbiota, how microbial metabolites influence the epithelium and the mucosal and peripheral immune system, and how the immune system shapes microbial composition and metabolism. Finally, this review will look at how metabolites are involved in cross‐talk between different members of the microbiota and their role during infections.

Telmisartan Influences the Antiproliferative Activity of Linoleic Acid in Human Colon Cancer Cells

Aim: Linoleic acid (LA) and telmisartan as PPARgamma agonists exhibit anticancer activity. The LA effect is observed for high non-achievable in vivo concentrations and in short treatment period, therefore we evaluate the effect of supplemental LA and pharmacological telmisartan plasma concentrations on human primary (SW480) and metastatic (SW620) colon cancer cells and immortal keratinocytes (HaCaT) cells in long-term treatment. Methods: Cell viability and proliferation were determined by TB and MTT and pro-apoptotic effect was measured by Annexin V binding assays, respectively.Results: LA decreased cancer cell viability and proliferation in a concentration-dependent manner, whereas no significant effect was found for HaCaT cells. Telmisartan (0.2 µM) suppresses antiproliferative effect of 60 µM LA on cancer cells in short-term treatment. Long-term administration of 60 µM LA reduced cancer cells viability after one week, while telmisartan delayed this effect by two weeks. Growth of all cell lines with 20 µM LA was unchanged during all treatment time. Telmisartan decreased late apoptosis of cancer and normal cells with 60 and 120 µM LA. Conclusion: The cytotoxic LA action depends not only on its concentration but also duration of treatment. Telmisartan exhibits biphasic but not synergistic effect on LA cytotoxicity in cancer cells.

Colonocyte metabolism shapes the gut microbiota

An imbalance in the colonic microbiota might underlie many human diseases, but the mechanisms that maintain homeostasis remain elusive. Recent insights suggest that colonocyte metabolism functions as a control switch, mediating a shift between homeostatic and dysbiotic communities. During homeostasis, colonocyte metabolism is directed toward oxidative phosphorylation, resulting in high epithelial oxygen consumption. The consequent epithelial hypoxia helps to maintain a microbial community dominated by obligate anaerobic bacteria, which provide benefit by converting fiber into fermentation products absorbed by the host. Conditions that alter the metabolism of the colonic epithelium increase epithelial oxygenation, thereby driving an expansion of facultative anaerobic bacteria, a hallmark of dysbiosis in the colon. Enteric pathogens subvert colonocyte metabolism to escape niche protection conferred by the gut microbiota. The reverse strategy, a metabolic reprogramming to restore colonocyte hypoxia, represents a promising new therapeutic approach for rebalancing the colonic microbiota in a broad spectrum of human diseases.

Healthy hosts rule within: ecological forces shaping the gut microbiota

A balanced gut microbiota is important for human health, but the mechanisms that maintain homeostasis are incompletely understood. Recent insights suggest the host plays a key role in shaping its gut microbiota to be beneficial. While host control in the small intestine curbs bacterial numbers to avoid competition for simple sugars and amino acids, the host limits oxygen availability in the large intestine to obtain microbial fermentation products from fiber. Epithelial cells are major players in imposing ecological control mechanisms, which involves the release of antimicrobial peptides by small-intestinal Paneth cells and maintenance of luminal anaerobiosis by epithelial hypoxia in the colon. Harnessing these epithelial control mechanisms for therapeutic means could provide a novel lynchpin for strategies to remediate dysbiosis.

Microbiota-activated PPAR-γ signaling inhibits dysbiotic Enterobacteriaceae expansion

Perturbation of the gut-associated microbial community may underlie many human illnesses, but the mechanisms that maintain homeostasis are poorly understood. We found that the depletion of butyrate-producing microbes by antibiotic treatment reduced epithelial signaling through the intracellular butyrate sensor peroxisome proliferator-activated receptor γ (PPAR-γ). Nitrate levels increased in the colonic lumen because epithelial expression of Nos2, the gene encoding inducible nitric oxide synthase, was elevated in the absence of PPAR-γ signaling. Microbiota-induced PPAR-γ signaling also limits the luminal bioavailability of oxygen by driving the energy metabolism of colonic epithelial cells (colonocytes) toward β-oxidation. Therefore, microbiota-activated PPAR-γ signaling is a homeostatic pathway that prevents a dysbiotic expansion of potentially pathogenic Escherichia and Salmonella by reducing the bioavailability of respiratory electron acceptors to Enterobacteriaceae in the lumen of the colon.

Loss of PTEN Facilitates Rosiglitazone-Mediated Enhancement of Platinum(IV) Complex LA-12-Induced Apoptosis in Colon Cancer Cells

We demonstrated for the first time an outstanding ability of rosiglitazone to mediate a profound enhancement of LA-12-induced apoptosis associated with activation of mitochondrial pathway in human colon cancer cells. This effect was preferentially observed in the G1 cell cycle phase, independent on p53 and PPARγ proteins, and accompanied with significant changes of selected Bcl-2 family protein levels. Further stimulation of cooperative synergic cytotoxic action of rosiglitazone and LA-12 was demonstrated in the cells deficient for PTEN, where mitochondrial apoptotic pathway was more stimulated and G1-phase-associated dying was reinforced. Our results suggest that combined treatment with rosiglitazone and LA-12 might be promising anticancer strategy in colon-derived tumours regardless of their p53 status, and also favourable in those defective in PTEN function.

Voluntary exercise protects against ulcerative colitis by up-regulating glucocorticoid-mediated PPAR-γ activity in the colon in mice

AIM

Voluntary exercise has been shown to protect against the development of ulcerative colitis, but the mechanism is not fully understood. We hypothesized that prior voluntary exercise would attenuate colonic inflammation and ameliorate clinical symptoms in dextran sulphate sodium (DSS)-induced ulcerative colitis by increasing glucocorticoid production and up-regulating PPAR-γ activity in the colon.

METHODS

Male C57Bl/6J mice were assigned to sedentary, exercise, exercise with PPAR-γ antagonist GW9662 or glucocorticoid synthesis inhibitor metyrapone. Following the completion of the 30 days' exercise training programme, they were treated with or without 2% DSS in drinking water for 5 days, followed by 5 days of regular water.

RESULTS

Compared with sedentary mice, exercise mice exhibited improved clinical symptoms (weight loss and diarrhoea) and less inflammation (expression of pro-inflammatory cytokines and histological injury) in response to DSS, whereas these beneficial effects were abolished by both GW9662 and metyrapone treatment. Molecular studies revealed that exercise significantly increased the expression of PPAR-γ, augmented the expression of steroidogenic enzymes (CYP11A1 and CYP11B1) and elevated corticosterone levels in the colon. GW9662 treatment reversed the expression of PPAR-γ without altering the expression of steroidogenic enzymes and corticosterone secretion in the colon, while metyrapone treatment blocked glucocorticoid secretion and abrogated the increase in PPAR-γ expression in the colon.

CONCLUSION

These findings suggest that prior voluntary exercise suppresses the expression of pro-inflammatory cytokines in the colon in response to inflammatory challenge by up-regulating glucocorticoid-mediated PPAR-γ activity, contributing to protection against the development of ulcerative colitis.

Effect of Proliferator-Activated Receptor-γ Pro12Ala Polymorphism on Colorectal Cancer Risk: A Meta-Analysis

Background

The association between peroxisome proliferators-activated receptor γ (PPARγ) Pro12Ala polymorphism and colorectal cancer (CRC) risk is still controversial. A meta-analysis was performed.

Material/Methods

We conducted a literature search using PubMed, EMBASE, and Cochran databases. The pooled odds ratio (OR) with 95% confidence intervals (CIs) were calculated. Fixed-effects and random-effects models were used. Dominant model, recessive model, and additive model were used in this meta-analysis.

Results

Fifteen studies including 13575 cases and 17085 controls were included in our meta-analysis. Result of this meta-analysis found that PPARγ Pro12Ala polymorphism was significantly associated with a reduced risk of CRC (OR=0.90; 95% CI 0.83–0.98; P=0.01). No significant association was found between PPARγ Pro12Ala polymorphism and CRC risk in Asians (OR=0.80; 95% CI 0.60–1.09; P=0.15). However, PPARγ Pro12Ala polymorphism was significantly associated with a reduced risk of CRC in Caucasians (OR=0.91; 95% CI 0.83–0.99; P=0.03). When stratified analysis was performed by CRC site, no positive association was found between PPARγ Pro12Ala polymorphism and rectal cancer (OR=0.95; 95% CI 0.74–1.22; P=0.71). However, a reduced risk of colon cancer was observed (OR=0.85; 95% CI 0.76–0.94; P=0.002).

Conclusions

In summary, this study suggests that PPARγ Pro12Ala polymorphism was a protective factor of CRC.

Amorfrutins Are Natural PPARγ Agonists with Potent Anti-inflammatory Properties

Amorfrutins are isoprenoid-substituted benzoic acid derivatives, which were found in Amorpha fruticosa L. (bastard indigo) and in Glycyrrhiza foetida Desf. (licorice). Recently, amorfrutins were shown to be selective activators of the nuclear receptor PPARγ. Here, we investigated the effects and PPARγ-based mechanisms of reducing inflammation in colon cells by treatment with amorfrutins. In TNF-α-stimulated colon cells amorfrutin A (1) reduced significantly the expression and secretion of several inflammation mediators, in part due to interaction with PPARγ. These results support the hypothesis that amorfrutins may have the potential to treat inflammation disorders such as chronic inflammatory bowel diseases.

Peroxisome proliferator-activated receptor gamma in the colon: inflammation and innate antimicrobial immunity

Peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor, originally described in adipose tissue, which controls the expression of a large number of regulatory genes in lipid metabolism and insulin sensitization. Well known by endocrinologists, thiazolidinedionesare classical PPARγ synthetic agonists, which were currently used as insulin-sensitizing agents in the treatment of type 2 diabetes. Although the clinical benefits of thiazolidinediones in treating metabolic disorders have been clearly demonstrated, studies performed in animal models of colitis and in patients with ulcerative colitis have also revealed the key roles of PPARγ activation in the regulation of inflammation and immune response, notably in the colon through epithelial cells.

Peroxisome proliferator-activated receptor γ upregulates galectin-9 and predicts prognosis in intestinal-type gastric cancer

The importance of PPARγ (peroxisome proliferator-activated receptor γ) in gastric cancer (GC) is unclear. We investigated the role of PPARγ in GC cell lines and an animal model, and its prognostic significance of PPARγ in GC patients. We controlled PPARγ and galectin-9 expression by using siRNAs and lentiviral constructs. Interaction between PPARγ and galectin-9 was evaluated using luciferase and chromatin immunoprecipitation assays. PPARγ expression in GCs was determined by immunohistochemical staining of tissue microarrays and survival analysis was done. Overexpression of PPARγ was accompanied by increased galectin-9. Enhanced PPARγ or galectin-9 expression increased E-cadherin expression; decreased expression of N-cadherin, fibronectin, snail, twist and slug and reduced cell invasion and migration. PPARγ bound to the galectin-9 promoter region. Galectin-9 activity increased in PPARγ-overexpressing cells but decreased in PPARγ siRNA-treated cells. In a zebrafish xenograft model, the number of migrated cancer cells and number of fish with AGS cells in the tail vein were reduced in PPARγ-overexpressing GC cells. PPARγ was expressed in 462 of the 688 patients (69.2%) with GC. In 306 patients with intestinal-type GC, those with PPARγ-positive tumors had lower overall and cancer-specific mortalities than those with PPARγ-negative tumors. PPARγ expression was an independent prognostic factor for overall and GC-specific mortality in patients with intestinal-type GC (adjusted hazard ratio, 0.42; 95% CI, 0.22-0.81). PPARγ inhibits cell invasion, migration and epithelial-mesenchymal transition through upregulation of galectin-9 in vitro and in vivo.

Can an oral antidiabetic (rosiglitazone) be of benefit in leukemia treatment?

PPARs are ligand-regulated transcription factors and regulate expression of several gene products. Therefore, PPARs are being studied for their possible contribution to the treatment of cancer, atherosclerosis, inflammation, infertility and demyelinating diseases. Primary AML patients were observed to have significantly elevated PPARγ mRNA expression compared to normal peripheral blood or bone marrow mononuclear cells. This study investigated the cytotoxic effects of rosiglitazone maleate, a pure PPARγ agonist, in vitro in HL-60 cell line. This study obtained results which can provide guidance for future studies. Whether the PPARy agonist rosiglitazone maleate may provide additive effects in refractory or relapsing cases of acute leukemia may be set as an objective for the future studies.

Deficiency of caveolin-1 in Apc(min/+) mice promotes colorectal tumorigenesis

Caveolin-1 (Cav1), a scaffold protein of membrane caveolae and coactivator of peroxisome proliferator-activated receptor gamma (PPARg), inhibits oncogenic signaling through Ras and wingless. However, the in vivo role of Cav1 in colorectal cancer (CRC) remained unknown. To test whether loss of Cav1 accelerates tumorigenesis, we generated a novel mouse model of CRC by crossing C57BL/6 Apc(min/+) with B6129 Cav1 knockout (Cav1-/-) mice. Apc(min/+) Cav1-/- mice developed large, microinvasive and vascularized intraepithelial adenocarcinomas in the distal colon and rectum with higher incidence than Apc(min/+) Cav1+/- and Apc(min/+) Cav1+/+ littermates. Intratumoral gene signatures related to Ras and wingless signaling were elevated, nuclear localization of PPARg protein and expression of PPARg-target genes were reduced independently of Cav1. The PPARg-agonist rosiglitazone prevented tumor formation in mice irrespectively of the Cav1 status and upregulated expression of the Ras-inhibitory protein docking protein-1. Thus, codeficiency of Cav1 and adenomatous polyposis coli facilitated formation of CRC, and activation of PPARg may offer novel strategies for treatment of CRC.

Genetic variation in peroxisome proliferator-activated receptor gamma, soy, and mammographic density in Singapore Chinese women

BACKGROUND

PPARγ is a transcription factor important for adipogenesis and adipocyte differentiation. Data from animal studies suggest that PPARγ may be involved in breast tumorigenesis, but results from epidemiologic studies on the association between PPARγ variation and breast cancer risk have been mixed. Recent data suggest that soy isoflavones can activate PPARγ. We investigated the interrelations of soy, PPARγ, and mammographic density, a biomarker of breast cancer risk in a cross-sectional study of 2,038 women who were members of the population-based Singapore Chinese Health Study Cohort.

METHODS

We assessed mammographic density using a computer-assisted method. We used linear regression to examine the association between 26 tagging single-nucleotide polymorphisms (SNP) of PPARγ and their interaction with soy intake and mammographic density. To correct for multiple testing, we calculated P values adjusted for multiple correlated tests (P(ACT)).

RESULTS

Out of the 26 tested SNPs in the PPARγ, seven SNPs were individually shown to be statistically significantly associated with mammographic density (P(ACT) = 0.008-0.049). A stepwise regression procedure identified that only rs880663 was independently associated with mammographic density which decreased by 1.89% per-minor allele (P(ACT) = 0.008). This association was significantly stronger in high-soy consumers as mammographic density decreased by 3.97% per-minor allele of rs880663 in high-soy consumers (P(ACT) = 0.006; P for interaction with lower soy intake = 0.017).

CONCLUSIONS

Our data support that PPARγ genetic variation may be important in determining mammographic density, particularly in high-soy consumers.

IMPACT

Our findings may help to identify molecular targets and lifestyle intervention for future prevention research.

SAMP1/YitFc mouse strain: a spontaneous model of Crohn's disease-like ileitis

The SAMP1/YitFc mouse strain represents a model of Crohn's disease (CD)-like ileitis that is ideal for investigating the pathogenesis of chronic intestinal inflammation. Different from the vast majority of animal models of colitis, the ileal-specific phenotype characteristic of SAMP1/YitFc mice occurs spontaneously, without genetic, chemical, or immunological manipulation. In addition, SAMP1/YitFc mice possess remarkable similarities to the human condition with regard to disease location, histologic features, incidence of extraintestinal manifestations, and response to conventional therapies. SAMP1/YitFc mice also display a well-defined time course of a predisease state and phases of acute and chronic ileitis. As such, the SAMP1/YitFc model is particularly suitable for elucidating pathways that precede the clinical phenotype that may lead to preventive, and therefore more efficacious, intervention with the natural course of disease, or alternatively, for the development of therapeutic strategies directed against chronic, established ileitis. In this review we summarize important contributions made by our group and others that uncover potential mechanisms in the pathogenesis of CD using this unique murine model of chronic intestinal inflammation.

Pathophysiological Roles of PPARgamma in Gastrointestinal Epithelial Cells

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

PPARgamma: The Portrait of a Target Ally to Cancer Chemopreventive Agents

Peroxisome proliferator-activated receptor-gamma (PPARγ), one of three ligand-activated transcription factors named PPAR, has been identified as a molecular target for cancer chemopreventive agents. PPARγ was initially understood as a regulator of adipocyte differentiation and glucose homeostasis while later on, it became evident that it is also involved in cell differentiation, apoptosis, and angiogenesis, biological processes which are deregulated in cancer. It is now established that PPARγ ligands can induce cell differentiation and yield early antineoplastic effects in several tumor types. Moreover, several bioactive natural products with cancer protecting potential are shown to operate through activation of PPARγ. Overall, PPARγ appears to be a prevalent target ally to cancer chemopreventive agents and therefore pursuing research in this area is of great relevance.

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.

Mycophenolic acid induces adipocyte-like differentiation and reversal of malignancy of breast cancer cells partly through PPARγ

Mycophenolic acid (MPA) has been known for decades to be an anticancer and immunosuppressive agent and has significant anticancer properties, but its underlying molecular mechanisms are poorly characterized. Peroxisome proliferator-activated receptor gamma (PPARγ) has a central role in adipocyte differentiation, and MPA has been shown to be a potent PPARγ agonist. Whether PPARγ activation has a putative role in the anticancer efficacy of MPA via induction of adipocyte-like differentiation has not been elucidated. In the present study, MPA was demonstrated to dose-dependently activate PPARγ transcription in the GAL4-hPPARγ (LBD) chimeric receptor assay and PPRE-luc reporter gene assay with an EC(50) of 5.2-9.3 μM. Treatment of the breast cancer cell lines MDA-MB-231 and MCF-7 with MPA resulted in differentiation of adipose tissue that was characterized by accumulation of intracellular lipids, enlargement of cell volume, and permanent withdrawal from the cell cycle at the G1/G0 stage. At a molecular level, the expression of three adipocyte differentiation markers (PPARγ, adipsin D, and aP2) was remarkably induced in differentiated breast cancer cells. However, RNA interference experiments showed that PPARγ-knockdown cannot completely reverse the differentiated state of MDA-MB-231 cells after MPA treatment. These data suggest that the effects of MPA on adipocyte-like terminal differentiation of breast cancer cells are (at least in part) due to PPARγ activation, which is a novel anticancer mechanism of MPA.

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.

Topical rosiglitazone treatment improves ulcerative colitis by restoring peroxisome proliferator-activated receptor-gamma activity

OBJECTIVES

Impaired epithelial expression of peroxisome proliferator-activated receptor-gamma (PPARgamma) has been described in animal colitis models and briefly in patients with ulcerative colitis, but the functional significance in humans is not well defined. We examined PPARgamma expression and functional activity in human colonic epithelium and explored the potential of topical treatment with rosiglitazone (a PPARgamma ligand) in patients with ulcerative colitis.

METHODS

Spontaneous and rosiglitazone-mediated PPARgamma and adipophillin expression (a gene transcriptionally activated by PPARgamma) were measured by reverse transcriptase PCR in colonic biopsies and isolated epithelial cells from patients with ulcerative colitis and controls. Fourteen patients with active distal ulcerative colitis were randomized to either rosiglitazone (4 mg) or mesalazine (1 g) enema treatment once daily for 14 days.

RESULTS

PPARgamma expression was fourfold reduced in epithelial cells from inflamed compared with uninflamed mucosa and controls. Adipophillin levels were decreased in parallel. Rosiglitazone induced a concentration-dependent increase in adipophillin levels and restored PPARgamma activity in epithelial cells from inflamed mucosa in vitro. Rosiglitazone enema treatment was well tolerated and reduced the Mayo ulcerative colitis score from 8.9 to 4.3 (P<0.01), similar to the effect of mesalazine. Rosiglitazone increased adipophillin levels in the epithelial cells of the patients, indicating PPARgamma activation in vivo.

CONCLUSIONS

Roziglitasone enemas improve impaired PPARgamma activity in inflamed colonic epithelium and have beneficial clinical effect in patients with active distal ulcerative colitis. These findings raise interest in further studies of PPARgamma ligands that exhibit their anti-inflammatory effect locally in the gut to avoid possible systemic side effects.

Enteric glia modulate epithelial cell proliferation and differentiation through 15-deoxy-12,14-prostaglandin J2

The enteric nervous system (ENS) and its major component, enteric glial cells (EGCs), have recently been identified as a major regulator of intestinal epithelial barrier functions. Indeed, EGCs inhibit intestinal epithelial cell (IEC) proliferation and increase barrier resistance and IEC adhesion via the release of EGC-derived soluble factors. Interestingly, EGC regulation of intestinal epithelial barrier functions is reminiscent of previously reported peroxisome proliferator-activated receptor gamma (PPARgamma)-dependent functional effects. In this context, the present study aimed at identifying whether EGC could synthesize and release the main PPARgamma ligand, 15-deoxy-(12,14)-prostaglandin J2 (15dPGJ2), and regulate IEC functions such as proliferation and differentiation via a PPARgamma dependent pathway. First, we demonstrated that the lipocalin but not the haematopoetic form for prostaglandin D synthase (PGDS), the enzyme responsible of 15dPGJ2 synthesis, was expressed in EGCs of the human submucosal plexus and of the subepithelium, as well as in rat primary culture of ENS and EGC lines. Next, 15dPGJ2 was identified in EGC supernatants of various EGC lines. 15dPGJ2 reproduced EGC inhibitory effects upon IEC proliferation, and inhibition of lipocalin PGDS expression by shRNA abrogated these effects. Furthermore, EGCs induced nuclear translocation of PPARgamma in IEC, and both EGC and 15dPGJ2 effects upon IEC proliferation were prevented by the PPARgamma antagonist GW9662. Finally, EGC induced differentiation-related gene expression in IEC through a PPARgamma-dependent pathway. Our results identified 15dPGJ2 as a novel glial-derived mediator involved in the control of IEC proliferation/differentiation through activation of PPARgamma. They also suggest that alterations of glial PGDS expression may modify intestinal epithelial barrier functions and be involved in the development of pathologies such as cancer or inflammatory bowel diseases.