Disruption of transforming growth factor-beta signaling by curcumin induces gene expression of peroxisome proliferator-activated receptor-gamma in rat hepatic stellate cells

The General Principle of the Warburg Effect as a Possible Approach for Cancer Immunotherapy: The Regulatory Effect of Plant Extracts Could Change the Game

The interpretation of the biochemistry of immune metabolism could be considered an attractive scientific field of biomedicine research. In this review, the role of glycolysis in macrophage polarization is discussed together with mitochondrial metabolism in cancer cells. In the first part, the focus is on the Warburg effect and redox metabolism during macrophage polarization, cancer development, and management of the immune response by the cancer cells. The second part addresses the possibility of impacts on the Warburg effect through targeting peroxisome proliferator-activated receptors (PPARs). This could be an activator of native immune responses. Because of the reported serious adverse effects of using synthetic ligands for PPARs in combination with chemotherapeutics, searches for less toxic and more active PPAR inhibitors, as well as blocking undesirable cellular PPAR-dependent processes, are in progress. On the other hand, recent research in modern immunotherapy has focused on the search for gentle immune-modulating natural compounds with harmless synergistic chemotherapeutic efficacy that can be used as an adjuvant. It is a well-known fact that the plant kingdom is a source of important therapeutic agents with multifaceted effectiveness. One of these is the known association with PPAR activities. In this regard, the secondary metabolites extracted from plants could change the game.

Mechanistic insight into the hepatoprotective effect of Moringa oleifera Lam leaf extract and telmisartan against carbon tetrachloride-induced liver fibrosis: plausible roles of TGF-β1/SMAD3/SMAD7 and HDAC2/NF-κB/PPARγ pathways

The increasing prevalence and limited therapeutic options for liver fibrosis necessitates more medical attention. Our study aims to investigate the potential molecular targets by which Moringa oleifera Lam leaf extract (Mor) and/or telmisartan (Telm) alleviate carbon tetrachloride (CCl4)-induced liver fibrosis in rats. Liver fibrosis was induced in male Sprague-Dawley rats by intraperitoneal injection of 50% CCl4 (1 ml/kg) every 72 hours, for 8 weeks. Intoxicated rats with CCl4 were simultaneously orally administrated Mor (400 mg/kg/day for 8 weeks) and/or Telm (10 mg/kg/day for 8 weeks). Treatment of CCl4-intoxicated rats with Mor/Telm significantly reduced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities compared to CCl4 intoxicated group (P < 0.001). Additionally, Mor/Telm treatment significantly reduced the level of hepatic inflammatory, profibrotic, and apoptotic markers including; nuclear factor-kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α), transforming growth factor-βeta1 (TGF-β1), and caspase-3. Interestingly, co-treatment of CCl4-intoxicated rats with Mor/Telm downregulated m-RNA expression of histone deacetylase 2 (HDAC2) (71.8%), and reduced protein expression of mothers against decapentaplegic homolog 3 (p-SMAD3) (70.6%) compared to untreated animals. Mor/Telm regimen also elevated p-SMAD7 protein expression as well as m-RNA expression of peroxisome proliferator-activated receptor γ (PPARγ) (3.6 and 3.1 fold, respectively p < 0.05) compared to CCl4 intoxicated group. Histopathological picture of the liver tissue intoxicated with CCl4 revealed marked improvement by Mor/Telm co-treatment. Conclusively, this study substantiated the hepatoprotective effect of Mor/Telm regimen against CCl4-induced liver fibrosis through suppression of TGF-β1/SMAD3, and HDAC2/NF-κB signaling pathways and up-regulation of SMAD7 and PPARγ expression.

Peroxisome proliferator-activated receptor gamma as a therapeutic target for hepatocellular carcinoma: Experimental and clinical scenarios

Hepatocellular carcinoma (HCC) is the most common type of liver cancer worldwide. Viral hepatitis is a significant risk factor for HCC, although metabolic syndrome and diabetes are more frequently associated with the HCC. With increasing prevalence, there is expected to be > 1 million cases annually by 2025. Therefore, there is an urgent need to establish potential therapeutic targets to cure this disease. Peroxisome-proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcription factor that plays a crucial role in the patho-physiology of HCC. Many synthetic agonists of PPARγ suppress HCC in experimental studies and clinical trials. These synthetic agonists have shown promising results by inducing cell cycle arrest and apoptosis in HCC cells and preventing the invasion and metastasis of HCC. However, some synthetic agonists also pose severe side effects in addition to their therapeutic efficacy. Thus natural PPARγ agonists can be an alternative to exploit this potential target for HCC treatment. In this review, the regulatory role of PPARγ in the pathogenesis of HCC is elucidated. Furthermore, the experimental and clinical scenario of both synthetic and natural PPARγ agonists against HCC is discussed. Most of the available literature advocates PPARγ as a potential therapeutic target for the treatment of HCC.

Phytochemicals: Potential Therapeutic Modulators of Radiation Induced Signaling Pathways

Ionizing radiation results in extensive damage to biological systems. The massive amount of ionizing radiation from nuclear accidents, radiation therapy (RT), space exploration, and the nuclear battlefield leads to damage to biological systems. Radiation injuries, such as inflammation, fibrosis, and atrophy, are characterized by genomic instability, apoptosis, necrosis, and oncogenic transformation, mediated by the activation or inhibition of specific signaling pathways. Exposure of tumors or normal cells to different doses of ionizing radiation could lead to the generation of free radical species, which can release signal mediators and lead to harmful effects. Although previous FDA-approved agents effectively mitigate radiation-associated toxicities, their use is limited due to their high cellular toxicities. Preclinical and clinical findings reveal that phytochemicals derived from plants that exhibit potent antioxidant activities efficiently target several signaling pathways. This review examined the prospective roles played by some phytochemicals in altering signal pathways associated with radiation response.

PPARG Drives Molecular Networks as an Inhibitor for the Pathologic Development and Progression of Lung Adenocarcinoma

Previous studies showed that low PPARG expression was associated with poor prognosis of lung adenocarcinoma (LA) with limited mechanisms identified. We first conducted a large-scale literature-based data mining to identify potential molecular pathways where PPARG could exert influence on the pathological development of LA. Then a mega-analysis using 13 independent LA expression datasets and a Pathway Enrichment Analysis (PEA) was conducted to study the gene expression levels and the functionalities of PPARG and the PPARG-driven triggers within the molecular pathways. Finally, a protein-protein interaction (PPI) network was established to reveal the functional connection between PPARG and its driven molecules. We identified 25 PPARG-driven molecule triggers forming multiple LA-regulatory pathways. Mega-analysis using 13 LA datasets supported these pathways and confirmed the downregulation of PPARG in the case of LA (p = 1.07e⁻⁰⁵). Results from the PEA and PPI analysis suggested that PPARG might inhibit the development of LA through the regulation of tumor cell proliferation and transmission-related molecules, including an LA tumor cell suppressor MIR145. Our results suggested that increased expression of PPARG could drive multiple molecular triggers against the pathologic development and prognosis of LA, indicating PPARG as a valuable therapeutic target for LA treatment.

The role and function of PPARγ in bladder cancer

Peroxisome proliferator-activated receptor gamma (PPARγ), a member of the nuclear receptor superfamily, participates in multiple physiological and pathological processes. Extensive studies have revealed the relationship between PPARγ and various tumors. However, the expression and function of PPARγ in bladder cancer seem to be controversial. It has been demonstrated that PPARγ affects the occurrence and progression of bladder cancer by regulating proliferation, apoptosis, metastasis, and reactive oxygen species (ROS) and lipid metabolism, probably through PPARγ-SIRT1 feedback loops, the PI3K-Akt signaling pathway, and the WNT/β-catenin signaling pathway. Considering the frequent relapses after chemotherapy, some researchers have focused on the relationship between PPARγ and chemotherapy sensitivity in bladder cancer. Moreover, the feasibility of PPARγ ligands as potential therapeutic targets for bladder cancer has been uncovered. Taken together, this review summarizes the relevant literature and our findings to explore the complicated role and function of PPARγ in bladder cancer.

Therapeutic potential of PPARγ natural agonists in liver diseases

Peroxisome proliferator‐activated receptor gamma (PPARγ) is a vital subtype of the PPAR family. The biological functions are complex and diverse. PPARγ plays a significant role in protecting the liver from inflammation, oxidation, fibrosis, fatty liver and tumours. Natural products are a promising pool for drug discovery, and enormous research effort has been invested in exploring the PPARγ‐activating potential of natural products. In this manuscript, we will review the research progress of PPARγ agonists from natural products in recent years and probe into the application potential and prospects of PPARγ natural agonists in the therapy of various liver diseases, including inflammation, hepatic fibrosis, non‐alcoholic fatty liver and liver cancer.

TGF-β in fibrosis by acting as a conductor for contractile properties of myofibroblasts

Myofibroblasts are non-muscle contractile cells that play a key physiologically role in organs such as the stem villi of the human placenta during physiological pregnancy. They are able to contract and relax in response to changes in the volume of the intervillous chamber. Myofibroblasts have also been observed in several diseases and are involved in wound healing and the fibrotic processes affecting several organs, such as the liver, lungs, kidneys and heart. During the fibrotic process, tissue retraction rather than contraction is correlated with collagen synthesis in the extracellular matrix, leading to irreversible fibrosis and, finally, apoptosis of myofibroblasts. The molecular motor of myofibroblasts is the non-muscle type IIA and B myosin (NMMIIA and NMMIIB). Fibroblast differentiation into myofibroblasts is largely governed by the transforming growth factor-β1 (TGF-β1). This system controls the canonical WNT/β-catenin pathway in a positive manner, and PPARγ in a negative manner. The WNT/β-catenin pathway promotes fibrosis, while PPARγ prevents it. This review focuses on the contractile properties of myofibroblasts and the conductor, TGF-β1, which together control the opposing interplay between PPARγ and the canonical WNT/β-catenin pathway.

Curcumin-Gene Expression Response in Hormone Dependent and Independent Metastatic Prostate Cancer Cells

The androgen receptor is one of the key targets for prostate cancer treatment. Despite its less satisfactory effects, chemotherapy is the most common treatment option for metastatic and/or castration-resistant patients. There are constant needs for novel anti-prostate cancer therapeutic/prevention agents. Curcumin, a known chemo-preventive agent, was shown to inhibit prostate cancer cell growth. This study aimed to unravel the inhibitory effect of curcumin in prostate cancer through analyzing the alterations of expressions of curcumin targeting genes clusters in androgen-dependent LNCaP cells and androgen-independent metastatic C4-2B cells. Hierarchical clustering showed the highest number of differentially expressed genes at 12 h post treatment in both cells, suggesting that the androgen-dependent/independent manner of curcumin impacts on prostate cancer cells. Evaluation of significantly regulated top canonical pathways highlighted that Transforming growth factor beta (TGF-β), Wingless-related integration site (Wnt), Phosphoinositide 3-kinase/Protein Kinase B/ mammalian target of rapamycin (PIK3/AKT(PKB)/mTOR), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) signaling were primarily inhibited, and Phosphatase and tensin homolog (PTEN) dependent cell cycle arrest and apoptosis pathways were elevated with curcumin treatment. The short term (3–24 h) and long term (48 h) effect of curcumin treatment revealed 31 and four genes modulated in both cell lines. TGF-β signaling, including the androgen/TGF-β inhibitor Prostate transmembrane protein androgen-induced 1 (PMEPA1), was the only pathway impacted by curcumin treatment after 48 h. Our findings also established that MYC Proto-Oncogene, basic helix-loop-helix (bHLH) Transcription Factor (MYC) signaling was down-regulated in curcumin-treated cell lines. This study established, for the first time, novel gene-networks and signaling pathways confirming the chemo-preventive and cancer-growth inhibitory nature of curcumin as a natural anti-prostate cancer compound.

Micro-Particle Curcumin for the Treatment of Chronic Kidney Disease-1: Study Protocol for a Multicenter Clinical Trial

Background

The progression to end-stage renal disease (ESRD) is the most important complication of chronic kidney disease (CKD). Patients with ESRD require dialysis or transplantation to survive, incur numerous complications, and have high mortality rates. Slowing the progression of CKD is an important goal. Unfortunately, even when current treatments are appropriately applied, patients with CKD still progress to ESRD. Current treatments do not address the inflammation and fibrosis that mediate progression to ESRD, but micro-particle curcumin, a natural health product, has both anti-inflammatory and anti-fibrotic properties and may be an effective treatment for patients with CKD.

Objective

Micro-particle curcumin for the treatment of CKD-1 (MPAC-CKD-1) will measure the effect of micro-particle curcumin on 2 important markers of CKD progression: albuminuria and estimated glomerular filtration rate (eGFR). Efficacy in either of these markers will justify a larger, international trial to investigate micro-particle curcumin's ability to lower the risk of ESRD in patients with CKD.

Design

MPAC-CKD-1 is a multicenter, double-blind prospective randomized controlled trial.

Setting

Four kidney disease clinics in Ontario, Canada (3 in London and 1 in Hamilton).

Patients

We will enroll patients with CKD, defined by an eGFR between 15 and 60 mL/min/1.73 m² and a daily albumin excretion of more than 300 mg (or a random urine sample albumin-to-creatinine ratio more than 30 mg/mmol).

Measurements

We will measure changes in the co-primary outcomes of urinary albumin-to-creatinine ratio and eGFR at 3 months and 6 months. We will also measure compliance, safety parameters, and changes in health-related quality of life.

Methods

Participants will be randomly assigned to receive micro-particle curcumin 90 mg once daily or matching placebo for 6 months. We will enroll at least 500 patients to exclude clinically meaningful 6-month changes in these 2 co-primary outcomes (16% difference in albuminuria, and a 2.3 mL/min/1.73 m² between-group difference in the 6-month change in eGFR, at a two-tailed alpha of 0.025, power of 0.80).

Results

Patient enrollment began on October 1, 2015, with 414 participants randomized as of July 2018. We expect to report the results in 2020.

Limitations

MPAC-CKD-1 is not powered to assess outcomes such as the need for renal replacement therapy or death.

Conclusions

MPAC-CKD-1 is a multicenter, double-blind prospective randomized controlled trial designed to test whether micro-particle curcumin reduces albuminuria and slows eGFR decline in patients with albuminuric CKD. MPAC-CKD-1 will also test the feasibility of this intervention and inform the need for a future larger scale trial (MPAC-CKD-2).

Trial registration

MPAC-CKD-1 is registered with U.S. National Institutes of Health at clinicaltrials.gov (NCT02369549). Protocol version 2.0, December 6, 2014.

New Concepts on Reversibility and Targeting of Liver Fibrosis; A Review Article

Currently, liver fibrosis and its complications are regarded as critical health problems. With the studies showing the reversible nature of liver fibrogenesis, scientists have focused on understanding the underlying mechanism of this condition in order to develop new therapeutic strategies. Although hepatic stellate cells are known as the primary cells responsible for liver fibrogenesis, studies have shown contributing roles for other cells, pathways, and molecules in the development of fibrosis depending on the etiology of liver fibrosis. Hence, interventions could be directed in the proper way for each type of liver diseases to better address this complication. There are two main approaches in clinical reversion of liver fibrosis; eliminating the underlying insult and targeting the fibrosis process, which have variable clinical importance in the treatment of this disease. In this review, we present recent concepts in molecular pathways of liver fibrosis reversibility and their clinical implications.

Peroxisome proliferator-activated receptor-γ and its related pathway in bone marrow mesenchymal stem cell differentiation co-cultured with mechanically stretched ligament fibroblasts

The occurrence of pelvic floor dysfunctional disease (PFD) is closely related with elasticity, toughness, and functional changes of the connective tissue of the pelvic support tissue. Bone marrow mesenchymal stem cells (BMSCs) have been confirmed to have the capacity to differentiate into a variety of cell types such as osteoblasts, chondroblasts, adipocytes and fibroblasts. Therefore, BMSCs have the potential to improve the clinical outcomes for PFD. Peroxisome proliferator-activated receptor-γ (PPAR-γ), a ligand activated transcription factor, has acquired a great deal of attention as it is involved in the fibrosis and cell differentiation. However, how it is regulated during the process of the differentiation of BMSCs into fibroblasts remains to be defined. The present study investigated the underlying mechanisms of PPAR-γ effect of mechanical stretch on the differentiation of BMSCs induced by pelvic ligament fibroblasts. PPAR-γ expression was decreased during the differentiation of BMSCs into fibroblasts by co-cultured stretched fibroblasts. Addition of transforming growth factor-β1 (TGF-β1) reduced PPAR-γ expression and promoted the differentiation of BMSCs. With the employment of endogenous ligand, activation of PPAR-γ suppressed the BMSC differentiation. Similar effects were also observed with overexpression of PPAR-γ gene. In addition, decrease of PPAR-γ by the use of shRNA targeting rat PPAR-γ significantly contributed to BMSC differentiation to fibroblasts. These results indicate that PPAR-γ negatively regulates the differentiation of BMSCs into fibroblasts.

Interactions between TGF-β1, canonical WNT/β-catenin pathway and PPAR γ in radiation-induced fibrosis

Radiation therapy induces DNA damage and inflammation leading to fibrosis. Fibrosis can occur 4 to 12 months after radiation therapy. This process worsens with time and years. Radiation-induced fibrosis is characterized by fibroblasts proliferation, myofibroblast differentiation, and synthesis of collagen, proteoglycans and extracellular matrix. Myofibroblasts are non-muscle cells that can contract and relax. Myofibroblasts evolve towards irreversible retraction during fibrosis process. In this review, we discussed the interplays between transforming growth factor-β1 (TGF-β1), canonical WNT/β-catenin pathway and peroxisome proliferator-activated receptor gamma (PPAR γ) in regulating the molecular mechanisms underlying the radiation-induced fibrosis, and the potential role of PPAR γ agonists. Overexpression of TGF-β and canonical WNT/β-catenin pathway stimulate fibroblasts accumulation and myofibroblast differentiation whereas PPAR γ expression decreases due to the opposite interplay of canonical WNT/β-catenin pathway. Both TGF-β1 and canonical WNT/β-catenin pathway stimulate each other through the Smad pathway and non-Smad pathways such as phosphatidylinositol 3-kinase/serine/threonine kinase (PI3K/Akt) signaling. WNT/β-catenin pathway and PPAR γ interact in an opposite manner. PPAR γ agonists decrease β-catenin levels through activation of inhibitors of the WNT pathway such as Smad7, glycogen synthase kinase-3 (GSK-3 β) and dickkopf-related protein 1 (DKK1). PPAR γ agonists also stimulate phosphatase and tensin homolog (PTEN) expression, which decreases both TGF-β1 and PI3K/Akt pathways. PPAR γ agonists by activating Smad7 decrease Smads pathway and then TGF-β signaling leading to decrease radiation-induced fibrosis. TGF-β1 and canonical WNT/β-catenin pathway promote radiation-induced fibrosis whereas PPAR γ agonists can prevent radiation-induced fibrosis.

Transforming growth factor β suppresses peroxisome proliferator-activated receptor γ expression via both SMAD binding and novel TGF-β inhibitory elements

Transforming growth factor β (TGF-β) contributes to wound healing and, when dysregulated, to pathological fibrosis. TGF-β and the anti-fibrotic nuclear hormone receptor peroxisome proliferator-activated receptor γ (PPARγ) repress each other's expression, and such PPARγ down-regulation is prominent in fibrosis and mediated, via previously unknown SMAD-signaling mechanisms. Here, we show that TGF-β induces the association of SMAD3 with both SMAD4, needed for translocation of the complex into the nucleus, and the essential context-sensitive co-repressors E2F4 and p107. The complex mediates TGF-β-induced repression by binding to regulatory elements in the target promoter. In the PPARG promoter, we found that the SMAD3-SMAD4 complex binds both to a previously unknown consensus TGF-β inhibitory element (TIE) and also to canonical SMAD-binding elements (SBEs). Furthermore, the TIE and SBEs independently mediated the partial repression of PPARG transcription, the first demonstration of a TIE and SBEs functioning within the same promoter. Also, TGF-β-treated fibroblasts contained SMAD complexes that activated a SMAD target gene in addition to those repressing PPARG transcription, the first finding of such dual activity within the same cell. These findings describe in detail novel mechanisms by which TGF-β represses PPARG transcription, thereby facilitating its own pro-fibrotic activity.

Management strategies for liver fibrosis

Liver fibrosis resulting from chronic liver injury are major causes of morbidity and mortality worldwide. Among causes of hepatic fibrosis, viral infection is most common (hepatitis B and C). In addition, obesity rates worldwide have accelerated the risk of liver injury due to nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Also liver fibrosis is associated with the consumption of alcohol, or autoimmune hepatitis and chronic cholangiophaties. The response of hepatocytes to inflammation plays a decisive role in the physiopathology of hepatic fibrosis, which involves the recruitment of both pro- and anti-inflammatory cells such as monocytes and macrophages. As well as the production of other cytokines and chemokines, which increase the stimulus of hepatic stellate cells by activating proinflammatory cells. The aim of this review is to identify the therapeutic options available for the treatment of the liver fibrosis, enabling the prevention of progression when is detected in time.

Ameliorative Effect of Curcumin-Encapsulated Hyaluronic Acid-PLA Nanoparticles on Thioacetamide-Induced Murine Hepatic Fibrosis

In this study, we developed curcumin-encapsulated hyaluronic acid–polylactide nanoparticles (CEHPNPs) to be used for liver fibrosis amelioration. CD44, the hyaluronic acid (HA) receptor, is upregulated on the surface of cancer cells and on activated hepatic stellate cells (aHSCs) rather than normal cells. CEHPNPs could bind to CD44 and be internalized effectively through endocytosis to release curcumin, a poor water-soluble liver protective agent. Thus, CEHPNPs were potentially not only improving drug efficiency, but also targeting aHSCs. HA and polylactide (PLA) were crosslinked by adipic acid dihydrazide (ADH). The synthesis of HA–PLA was monitored by Fourier-transform infrared (FTIR) and Nuclear Magnetic Resonance (NMR). The average particle size was approximately 60–70 nm as determined by dynamic light scattering (DLS) and scanning electron microscope (SEM). Zeta potential was around −30 mV, which suggested a good stability of the particles. This drug delivery system induced significant aHSC cell death without affecting quiescent HSCs, hepatic epithelial, and parenchymal cells. This system reduced drug dosage without sacrificing therapeutic efficacy. The cytotoxicity IC₅₀ (inhibitory concentration at 50%) value of CEHPNPs was approximately 1/30 to that of the free drug treated group in vitro. Additionally, the therapeutic effects of CEHPNPs were as effective as the group treated with the same curcumin dose intensity in vivo. CEHPNPs significantly reduced serum aspartate transaminase/alanine transaminase (ALT/AST) significantly, and attenuated tissue collagen production and cell proliferation as revealed by liver biopsy. Conclusively, the advantages of superior biosafety and satisfactory therapeutic effect mean that CEHPNPs hold great potential for treating hepatic fibrosis.

Diamond Nanoparticles Modify Curcumin Activity: In Vitro Studies on Cancer and Normal Cells and In Ovo Studies on Chicken Embryo Model

Curcumin has been studied broadly for its wide range of biological activities, including anticancer properties. The major problem with curcumin is its poor bioavailability, which can be improved by the addition of carriers, such as diamond nanoparticles (DN). They are carbon allotropes, and are therefore biocompatible and easily taken up by cells. DN are non-toxic and have antiangiogenic properties with potential applications in cancer therapy. Their large surface makes them promising compounds in a drug delivery system for bioactive agents, as DN create bio-complexes in a fast and simple process of self-organisation. We investigated the cytotoxicity of such bio-complexes against liver cancer cells and normal fibroblasts, revealing that conjugation of curcumin with DN significantly improves its activity. The experiment performed in a chicken embryo model demonstrated that neither curcumin nor DN nor bio-complexes affect embryo development, even though DN can form deposits in tissues. Preliminary results confirmed the applicability of DN as an efficient carrier of curcumin, which improves its performance against cancer cells in vitro, yet is not toxic to an organism, which makes the bio-complex a promising anticancer agent.

Curcumin inhibits cobalt chloride-induced epithelial-to-mesenchymal transition associated with interference with TGF-β/Smad signaling in hepatocytes

Epithelial-mesenchymal transition (EMT) occurs during adult tissue remodeling responses including carcinogenesis and fibrosis. Existing evidence reveals that hepatocytes can undergo EMT in adult liver, which is critically involved in chronic liver injury. We herein established a hypoxia-induced EMT model in human LO2 hepatocytes treated with cobalt chloride (CoCl2) in vitro, and evaluated the effects of curcumin, a natural antifibrotic compound, on hepatocyte EMT and explored the underlying molecular mechanisms. We found that CoCl2 at non-toxic doses induced a mesenchymal cell phenotype in hepatocytes and upregulated several mesenchymal markers including α-smooth muscle actin, vimentin, N-cadherin, fibronectin and Snail (an EMT-related transcription factor), but downregulated the epithelial marker E-cadherin in hepatocytes. However, curcumin reversed the morphological changes, abrogated the increased expression of mesenchymal markers, and rescued E-cadherin expression in CoCl2-treated hepatocytes, suggesting the inhibition of hepatocyte EMT in vitro. We further found that curcumin interfered with the transforming growth factor-β (TGF-β) signaling by reducing the expression of TGF-β receptor I and inhibiting the expression and phosphorylation of Smad2 and Smad3. Use of SB431542, a specific inhibitor of TGF-β receptor I, demonstrated that interference with the TGF-β/Smad pathway was associated with curcumin suppression of hepatocyte EMT. Our in vivo data showed that curcumin affected hepatic EMT in rat fibrotic liver caused by carbon tetrachloride, which was associated with the inhibition of TGF-β/Smad signaling. These findings characterized a novel mechanism by which curcumin modulated hepatocyte EMT implicated in treatment of liver fibrosis.

Curcumin regulates cell fate and metabolism by inhibiting hedgehog signaling in hepatic stellate cells

Accumulating evidence indicates that Hedgehog (Hh) signaling becomes activated in chronic liver injury and plays a role in the pathogenesis of hepatic fibrosis. Hepatic stellate cells (HSCs) are Hh-responsive cells and activation of the Hh pathway promotes transdifferentiation of HSCs into myofibroblasts. Targeting Hh signaling may be a novel therapeutic strategy for treatment of liver fibrosis. We previously reported that curcumin has potent antifibrotic effects in vivo and in vitro, but the underlying mechanisms are not fully elucidated. This study shows that curcumin downregulated Patched and Smoothened, two key elements in Hh signaling, but restored Hhip expression in rat liver with carbon tetrachloride-induced fibrosis and in cultured HSCs. Curcumin also halted the nuclear translocation, DNA binding, and transcription activity of Gli1. Moreover, the Hh signaling inhibitor cyclopamine, like curcumin, arrested the cell cycle, induced mitochondrial apoptosis, reduced fibrotic gene expression, restored lipid accumulation, and inhibited invasion and migration in HSCs. However, curcumin's effects on cell fate and fibrogenic properties of HSCs were abolished by the Hh pathway agonist SAG. Furthermore, curcumin and cyclopamine decreased intracellular levels of adenosine triphosphate and lactate, and inhibited the expression and/or function of several key molecules controlling glycolysis. However, SAG abrogated the curcumin effects on these parameters of glycolysis. Animal data also showed that curcumin downregulated glycolysis-regulatory proteins in rat fibrotic liver. These aggregated data therefore indicate that curcumin modulated cell fate and metabolism by disrupting the Hh pathway in HSCs, providing novel molecular insights into curcumin reduction of HSC activation.

Curcumin ameliorates renal fibrosis by inhibiting local fibroblast proliferation and extracellular matrix deposition

Renal fibrosis is mainly characterized by activation and proliferation of interstitial fibroblasts and by excessive synthesis and accumulation of extracellular matrix (ECM) components, including fibronectin (FN) and collagen. This study investigated the effects of curcumin on proliferation of renal interstitial fibroblasts and their underlying mechanisms in vivo and in vitro. ECM components were visualized by Sirius red and immunohistochemistry staining and quantified by western blot analysis in mice with unilateral ureteral obstruction (UUO). Duplex staining for proliferating cell nuclear antigen and α-smooth muscle actin (α-SMA), as well as MTT and flow cytometry assays, were performed to measure fibroblast proliferation. Protein expression of phosphorylated Smad2/3 (p-Smad2/3) and peroxisome proliferator-activated receptor-γ (PPAR-γ) were assessed by western blotting. Curcumin treatment decreased the accumulation of type I collagen and FN in the kidney of animals with UUO. Activation of rat renal interstitial fibroblasts (NRK-49F) was induced by TGF-β1. Curcumin treatment inhibited fibroblast proliferation and the cell cycle was arrested in the G1 phase. Curcumin treatment upregulated the expression of PPAR-γ and downregulated the expression of p-Smad2/3. These results suggest that curcumin treatment ameliorates renal fibrosis by reducing fibroblast proliferation and ECM accumulation mediated by PPAR-γ and Smad-dependent TGF-β1 signaling.

Liver fibrosis and protection mechanisms action of medicinal plants targeting apoptosis of hepatocytes and hepatic stellate cells

Following chronic liver injury, hepatocytes undergo apoptosis leading to activation of hepatic stellate cells (HSC). Consequently, activated HSC proliferate and produce excessive extracellular matrix, responsible for the scar formation. The pandemic trend of obesity, combined with the high incidence of alcohol intake and viral hepatitis infections, highlights the urgent need to find accessible antifibrotic therapies. Treatment strategies should take into account the versatility of its pathogenesis and act on all the cell lines involved to reduce liver fibrosis. Medicinal plants are achieving popularity as antifibrotic agents, supported by their safety, cost-effectiveness, and versatility. This review will describe the role of hepatocytes and HSC in the pathogenesis of liver fibrosis and detail the mechanisms of modulation of apoptosis of both cell lines by twelve known hepatoprotective plants in order to reduce liver fibrosis.

Nitrated fatty acids reverse pulmonary fibrosis by dedifferentiating myofibroblasts and promoting collagen uptake by alveolar macrophages

Idiopathic pulmonary fibrosis (IPF) is a progressive, fatal disease, thought to be largely transforming growth factor β (TGFβ) driven, for which there is no effective therapy. We assessed the potential benefits in IPF of nitrated fatty acids (NFAs), which are unique endogenous agonists of peroxisome proliferator-activated receptor γ (PPARγ), a nuclear hormone receptor that exhibits wound-healing and antifibrotic properties potentially useful for IPF therapy. We found that pulmonary PPARγ is down-regulated in patients with IPF. In vitro, knockdown or knockout of PPARγ expression in isolated human and mouse lung fibroblasts induced a profibrotic phenotype, whereas treating human fibroblasts with NFAs up-regulated PPARγ and blocked TGFβ signaling and actions. NFAs also converted TGFβ to inactive monomers in cell-free solution, suggesting an additional mechanism through which they may inhibit TGFβ. In vivo, treating mice bearing experimental pulmonary fibrosis with NFAs reduced disease severity. Also, NFAs up-regulated the collagen-targeting factor milk fat globule-EGF factor 8 (MFG-E8), stimulated collagen uptake and degradation by alveolar macrophages, and promoted myofibroblast dedifferentiation. Moreover, treating mice with established pulmonary fibrosis using NFAs reversed their existing myofibroblast differentiation and collagen deposition. These findings raise the prospect of treating IPF with NFAs to halt and perhaps even reverse the progress of IPF.

Curcumin eliminates the effect of advanced glycation end-products (AGEs) on the divergent regulation of gene expression of receptors of AGEs by interrupting leptin signaling

Non-alcoholic steatohepatitis (NASH) is a major risk factor for hepatic fibrogenesis. NASH is often found in diabetic patients with hyperglycemia. Hyperglycemia induces non-enzymatic glycation of proteins, yielding advanced glycation end-products (AGEs). Effects of AGEs are mainly mediated by two categories of cytoplasmic membrane receptors. Receptor for AGEs (RAGE) is associated with increased oxidative stress and inflammation, whereas AGE receptor-1 (AGE-R1) is involved in detoxification and clearance of AGEs. Activation of hepatic stellate cells (HSC) is crucial to the development of hepatic fibrosis. We recently reported that AGEs stimulated HSC activation likely by inhibiting gene expression of AGE-R1 and inducing gene expression of RAGE in HSC, which were eliminated by the antioxidant curcumin. This study is to test our hypothesis that curcumin eliminates the effects of AGEs on the divergent regulation of the two receptors of AGEs in HSC by interrupting the AGE-caused activation of leptin signaling, leading to the inhibition of HSC activation. We observed herein that AGEs activated leptin signaling by inducing gene expression of leptin and its receptor in HSC. Like AGEs, leptin differentially regulated gene expression of RAGE and AGE-R1. Curcumin eliminated the effects of AGEs in HSC by interrupting leptin signaling and activating transcription factor NF-E2 p45-related factor 2 (Nrf2), leading to the elevation of cellular glutathione and the attenuation of oxidative stress. In conclusions, curcumin eliminated the effects of AGEs on the divergent regulation of gene expression of RAGE and AGE-R1 in HSC by interrupting the AGE-caused activation of leptin signaling, leading to the inhibition of HSC activation.

Curcumin attenuates angiogenesis in liver fibrosis and inhibits angiogenic properties of hepatic stellate cells

Hepatic fibrosis is concomitant with sinusoidal pathological angiogenesis, which has been highlighted as novel therapeutic targets for the treatment of chronic liver disease. Our prior studies have demonstrated that curcumin has potent antifibrotic activity, but the mechanisms remain to be elucidated. The current work demonstrated that curcumin ameliorated fibrotic injury and sinusoidal angiogenesis in rat liver with fibrosis caused by carbon tetrachloride. Curcumin reduced the expression of a number of angiogenic markers in fibrotic liver. Experiments in vitro showed that the viability and vascularization of rat liver sinusoidal endothelial cells and rat aortic ring angiogenesis were not impaired by curcumin. These results indicated that hepatic stellate cells (HSCs) that are characterized as liver-specific pericytes could be potential target cells for curcumin. Further investigations showed that curcumin inhibited VEGF expression in HSCs associated with disrupting platelet-derived growth factor-β receptor (PDGF-βR)/ERK and mTOR pathways. HSC motility and vascularization were also suppressed by curcumin associated with blocking PDGF-βR/focal adhesion kinase/RhoA cascade. Gain- or loss-of-function analyses revealed that activation of peroxisome proliferator-activated receptor-γ (PPAR-γ) was required for curcumin to inhibit angiogenic properties of HSCs. We concluded that curcumin attenuated sinusoidal angiogenesis in liver fibrosis possibly by targeting HSCs via a PPAR-γ activation-dependent mechanism. PPAR-γ could be a target molecule for reducing pathological angiogenesis during liver fibrosis.

Curcumin Inhibits Prostate Cancer Bone Metastasis by Up-Regulating Bone Morphogenic Protein-7 in Vivo

A number of studies have focused on the beneficial properties of Curcumin (diferuloyl methane, used in South Asian cuisine and traditional medicine) such as the chemoprevention of cancer. Recent studies have also indicated that this material has significant benefits for the treatment of cancer and is currently undergoing several clinical trials. We have been interested in the application of this compound as a therapeutic agent for advanced prostate cancer, particularly the skeletal complications in this malignancy. Our earlier work indicated that this compound could inhibit the osteomimetic properties which occur in castration resistant prostate cancer cells, by interfering with the common denominators between these cancer cells and the bone cells in the metastatic tumor microenvironment, namely the osteoblasts and the osteoclast. We predicted that curcumin could break the vicious cycle of reciprocal stimulation that results in uncontrolled osteolysis in the bony matrix. In this work, we have evaluated the potential of this compound in inhibiting the bone metastasis of hormone refractory prostate cancer cells in an established animal model. Our results strongly suggest that curcumin modulates the TGF-β signaling that occurs due to bone matrix degradation by up-regulating the metastasis inhibitory bone morphogenic protein-7 (BMP- 7). This enhancement of BMP-7 in the context of TGF-βin the tumor microenvironment is shown to enhance the mesenchymal-to-epithelial transition. Most importantly, we show that as a result of BMP-7 up-regulation, a novel brown/beige adipogenic differentiation program is also up-regu- lated which plays a role in the inhibition of bone metastasis. Our results suggest that curcumin may subvert the TGF-βsignaling to an alternative adipogenic differentiation program in addition to the previously established interference with the osteomimetic properties, thus inhibiting the bone metastatic processes in a chemopreventive as well as therapeutic setting.

Peroxisome proliferator-activated receptor-γ interrupts angiogenic signal transduction by transrepression of platelet-derived growth factor-β receptor in hepatic stellate cells

Hepatic stellate cells (HSCs) are liver-specific pericytes that are recruited to vessels and secret pro-angiogenic cytokines, and thus actively involved in pathological vascularization during liver fibrosis. Peroxisome proliferator-activated receptor-γ (PPARγ) is a switch molecule controlling HSC activation. We investigated PPARγ regulation of angiogenic signal transduction and the molecular mechanisms involved in HSCs. Primary rat HSCs and liver sinusoidal endothelial cells (LSECs) were isolated and used in this study. Boyden chamber and tubulogenesis assays, identified that focal adhesion kinase (FAK)-RhoA signaling activated by platelet-derived growth factor (PDGF) was required for HSC motility and the associated vascularization. PDGF also stimulated vascular endothelial growth factor (VEGF) expression and HSC-driven vascularization through signals mediated by extracellular signal-regulated kinase (ERK) and mammalian target of rapamycin (mTOR). Gain- and loss-of-function analyses demonstrated that activation of PPARγ interrupted FAK-RhoA, ERK and mTOR cascades and inhibited HSC-based vascularization. Molecular evidence further revealed that PPARγ attenuation of HSC angiogenic properties was dependent on inhibition of PDGF-β receptor expression. We concluded that PPARγ inhibited angiogenic signal transduction through transrepression of PDGF-β receptor leading to reduced HSC motility, reduced VEGF expression, and thereby attenuated HSC-driven angiogenesis. PPARγ could be a molecular target for preventing vascular remolding in hepatic fibrosis.

Curcumin modulates cannabinoid receptors in liver fibrosis in vivo and inhibits extracellular matrix expression in hepatic stellate cells by suppressing cannabinoid receptor type-1 in vitro

Activation of hepatic stellate cells (HSCs) is a pivotal event leading to extracellular matrix (ECM) overproduction during hepatic fibrogenesis. Compelling evidence indicates that cannabinoid receptors (CBRs) play an important role in chronic liver disease. Antagonism of hepatic CBR type 1 (CBR1) could be a novel therapeutic strategy for liver fibrosis. Our previous studies have demonstrated that curcumin has potent antifibrotic activity, but the mechanisms remain to be elucidated. The current work was to examine the curcumin effect on CBRs system and its relevance to inhibition of ECM expression in HSCs. Our in vivo data demonstrated that curcumin ameliorated fibrotic injury, and downregulated CBR1 but upregulated CBR2 at both mRNA and protein levels in rat fibrotic liver caused by carbon tetrachloride. The subsequent in vitro investigations showed that curcumin reduced the mRNA and protein abundance of CBR1 in cultured HSCs and decreased the expression of three critical ECM proteins. Further analyses revealed that CBR1 agonist abrogated the curcumin inhibition of ECM expression, but CBR1 antagonist mimicked and reinforced the curcumin effects. Autodock simulations predicted that curcumin could bind to CBR1 with two hydrogen bonds. Collectively, our current studies revealed that curcumin reduction of liver fibrosis was associated with modulation of CBRs system and that antagonism of CBR1 contributed to curcumin inhibition of ECM expression in HSCs.

Curcumin protects the developing lung against long-term hyperoxic injury

Curcumin, a potent anti-inflammatory and antioxidant agent, modulates peroxisome proliferator-activated receptor-γ signaling, a key molecule in the etiology of bronchopulmonary dysplasia (BPD). We have previously shown curcumin's acute protection against neonatal hyperoxia-induced lung injury. However, its longer-term protection against BPD is not known. Hypothesizing that concurrent treatment with curcumin protects the developing lung against hyperoxia-induced lung injury long-term, we determined if curcumin protects against hyperoxic neonatal rat lung injury for the first 5 days of life, as determined at postnatal day (PND) 21. One-day-old rat pups were exposed to either 21 or 95% O₂ for 5 days with or without curcumin treatment (5 mg/kg) administered intraperitoneally one time daily, following which the pups grew up to PND21 in room air. At PND21 lung development was determined, including gross and cellular structural and functional effects, and molecular mediators of inflammatory injury. To gain mechanistic insights, embryonic day 19 fetal rat lung fibroblasts were examined for markers of apoptosis and MAP kinase activation following in vitro exposure to hyperoxia for 24 h in the presence or absence of curcumin (5 μM). Curcumin effectively blocked hyperoxia-induced lung injury based on systematic analysis of markers for lung injury (apoptosis, Bcl-2/Bax, collagen III, fibronectin, vimentin, calponin, and elastin-related genes) and lung morphology (radial alveolar count and alveolar septal thickness). Mechanistically, curcumin prevented the hyperoxia-induced increases in cleaved caspase-3 and the phosphorylation of Erk1/2. Molecular effects of curcumin, both structural and cytoprotective, suggest that its actions against hyperoxia-induced lung injury are mediated via Erk1/2 activation and that it is a potential intervention against BPD.

Curcumin modulates the inflammatory response and inhibits subsequent fibrosis in a mouse model of viral-induced acute respiratory distress syndrome

Acute Respiratory Distress Syndrome (ARDS) is a clinical syndrome characterized by diffuse alveolar damage usually secondary to an intense host inflammatory response of the lung to a pulmonary or extrapulmonary infectious or non-infectious insult often leading to the development of intra-alveolar and interstitial fibrosis. Curcumin, the principal curcumoid of the popular Indian spice turmeric, has been demonstrated as an anti-oxidant and anti-inflammatory agent in a broad spectrum of diseases. Using our well-established model of reovirus 1/L-induced acute viral pneumonia, which displays many of the characteristics of the human ALI/ARDS, we evaluated the anti-inflammatory and anti-fibrotic effects of curcumin. Female CBA/J mice were treated with curcumin (50 mg/kg) 5 days prior to intranasal inoculation with 10(7)pfu reovirus 1/L and daily, thereafter. Mice were evaluated for key features associated with ALI/ARDS. Administration of curcumin significantly modulated inflammation and fibrosis, as revealed by histological and biochemical analysis. The expression of IL-6, IL-10, IFNγ, and MCP-1, key chemokines/cytokines implicated in the development of ALI/ARDS, from both the inflammatory infiltrate and whole lung tissue were modulated by curcumin potentially through a reduction in the phosphorylated form of NFκB p65. While the expression of TGFß1 was not modulated by curcumin, TGFß Receptor II, which is required for TGFß signaling, was significantly reduced. In addition, curcumin also significantly inhibited the expression of α-smooth muscle actin and Tenascin-C, key markers of myofibroblast activation. This data strongly supports a role for curcumin in modulating the pathogenesis of viral-induced ALI/ARDS in a pre-clinical model potentially manifested through the alteration of inflammation and myofibroblast differentiation.

Peroxisome proliferator-activated receptor-γ as a therapeutic target for hepatic fibrosis: from bench to bedside

Hepatic fibrosis is a dynamic chronic liver disease occurring as a consequence of wound-healing responses to various hepatic injuries. This disorder is one of primary predictors for liver-associated morbidity and mortality worldwide. To date, no pharmacological agent has been approved for hepatic fibrosis or could be recommended for routine use in clinical context. Cellular and molecular understanding of hepatic fibrosis has revealed that peroxisome proliferator-activated receptor-γ (PPARγ), the functioning receptor for antidiabetic thiazolidinediones, plays a pivotal role in the pathobiology of hepatic stellate cells (HSCs), whose activation is the central event in the pathogenesis of hepatic fibrosis. Activation of PPARγ inhibits HSC collagen production and modulates HSC adipogenic phenotype at transcriptional and epigenetic levels. These molecular insights indicate PPARγ as a promising drug target for antifibrotic chemotherapy. Intensive animal studies have demonstrated that stimulation of PPARγ regulatory system through gene therapy approaches and PPARγ ligands has therapeutic promise for hepatic fibrosis induced by a variety of etiologies. At the same time, thiazolidinedione agents have been investigated for their clinical benefits primarily in patients with nonalcoholic steatohepatitis, a common metabolic liver disorder with high potential to progress to fibrosis and liver-related death. Although some studies have shown initial promise, none has established long-term efficacy in well-controlled randomized clinical trials. This comprehensive review covers the 10-year discoveries of the molecular basis for PPARγ regulation of HSC pathophysiology and then focuses on the animal investigations and clinical trials of various therapeutic modalities targeting PPARγ for hepatic fibrosis.

Dietary fat level affects tissue iron levels but not the iron regulatory gene HAMP in rats

Because dietary fats affect the regulation and use of body iron, we hypothesized that iron regulatory and transport genes may be affected by dietary fat. A model of early-stage I to II, nonalcoholic fatty liver was used in which rats were fed standard (35% energy from fat) or high-fat (71% energy from fat) liquid diets with normal iron content (STD/HF groups). In addition, intraperitoneal injections of iron dextran were given to iron-loaded (STD+/HF+ groups) and iron-deficient diets to STD-/HF- groups. Plasma osmolality, hemoglobin level, and mean corpuscular hemoglobin concentration were increased in all STD diet groups compared with all HF diet groups. Plasma iron and transferrin saturation were affected by an interaction between dietary fat and iron. They were high in the STD group (normal iron) compared with their respective HF group. Similarly, this group also showed a 4-fold increase in the messenger RNA expression of the hepatic hemochromatosis gene. Spleen iron was high in the iron-loaded STD+ group compared with all other groups. Hepatic iron and messenger RNA expression of peroxisome proliferator-activated receptor-γ, CCAAT/enhancer binding protein α, interleukin-6, and iron transport genes (transferrin receptor 2, divalent metal transporter 1 iron-responsive element, and divalent metal transporter 1 non-iron-responsive element) were increased, whereas tumor necrosis factor α was decreased in the HF diet groups. The expression of iron regulatory gene HAMP was not increased in the HF diet groups. Iron regulatory and transport genes involved in cellular and systemic iron homeostasis may be affected by the macronutrient composition of the diet.

Curcumin inhibits gene expression of receptor for advanced glycation end-products (RAGE) in hepatic stellate cells in vitro by elevating PPARγ activity and attenuating oxidative stress

BACKGROUND AND PURPOSE

Diabetes is characterized by hyperglycaemia, which facilitates the formation of advanced glycation end-products (AGEs). Type 2 diabetes mellitus is commonly accompanied by non-alcoholic steatohepatitis, which could lead to hepatic fibrosis. Receptor for AGEs (RAGE) mediates effects of AGEs and is associated with increased oxidative stress, cell growth and inflammation. The phytochemical curcumin inhibits the activation of hepatic stellate cells (HSCs), the major effectors during hepatic fibrogenesis. The aim of this study was to explore the underlying mechanisms of curcumin in the elimination of the stimulating effects of AGEs on the activation of HSCs. We hypothesize that curcumin eliminates the effects of AGEs by suppressing gene expression of RAGE.

EXPERIMENTAL APPROACH

Gene promoter activities were evaluated by transient transfection assays. The expression of rage was silenced by short hairpin RNA. Gene expression was analysed by real-time PCR and Western blots. Oxidative stress was evaluated.

KEY RESULTS

AGEs induced rage expression in cultured HSCs, which played a critical role in the AGEs-induced activation of HSCs. Curcumin at 20 µM eliminated the AGE effects, which required the activation of PPARγ. In addition, curcumin attenuated AGEs-induced oxidative stress in HSCs by elevating the activity of glutamate-cysteine ligase and by stimulating de novo synthesis of glutathione, leading to the suppression of gene expression of RAGE.

CONCLUSION AND IMPLICATIONS

Curcumin suppressed gene expression of RAGE by elevating the activity of PPARγ and attenuating oxidative stress, leading to the elimination of the AGE effects on the activation of HSCs.

LINKED ARTICLE

This article is commented on by Stefanska, pp. 2209-2211 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2012.01959.x.

Modulation of PPAR-γ by Nutraceutics as Complementary Treatment for Obesity-Related Disorders and Inflammatory Diseases

A direct correlation between adequate nutrition and health is a universally accepted truth. The Western lifestyle, with a high intake of simple sugars, saturated fat, and physical inactivity, promotes pathologic conditions. The main adverse consequences range from cardiovascular disease, type 2 diabetes, and metabolic syndrome to several cancers. Dietary components influence tissue homeostasis in multiple ways and many different functional foods have been associated with various health benefits when consumed. Natural products are an important and promising source for drug discovery. Many anti-inflammatory natural products activate peroxisome proliferator-activated receptors (PPAR); therefore, compounds that activate or modulate PPAR-gamma (PPAR-γ) may help to fight all of these pathological conditions. Consequently, the discovery and optimization of novel PPAR-γ agonists and modulators that would display reduced side effects is of great interest. In this paper, we present some of the main naturally derived products studied that exert an influence on metabolism through the activation or modulation of PPAR-γ, and we also present PPAR-γ-related diseases that can be complementarily treated with nutraceutics from functional foods.

Organ fibrosis inhibited by blocking transforming growth factor-β signaling via peroxisome proliferator-activated receptor γ agonists

BACKGROUND

Organ fibrosis has been viewed as one of the major medical problems, which can lead to progressive dysfunction of the liver, lung, kidney, skin, heart, and eventually death of patients. Fibrosis is initiated by a variety of pathological, physiological, biochemical, and physical factors. Regardless of their different etiologies, they all share a common pathogenetic process: excessive activation of the key profibrotic cytokine, transforming growth factor-beta (TGF-beta). Peroxisome proliferator-activated receptor gamma (PPARgamma), a ligand-activated transcription factor of the nuclear receptor superfamily, has received particular attention in recent years, because the activation of PPARgamma by both natural and synthetic agonists could effectively inhibit TGF-beta-induced profibrotic effects in many organs.

DATA SOURCES

The English-language medical databases, PubMed, Elsevier and SpringerLink were searched for articles on PPARgamma, TGF-beta, and fibrosis, and related topics.

RESULTS

TGF-beta is recognized as a key profibrotic cytokine. Excessive activation of TGF-beta increases synthesis of extracellular matrix proteins and decreases their degradation, associated with a gradual destruction of normal tissue architecture and function, whereas PPARgamma agonists inhibit TGF-beta signal transduction and are effective antifibrogenic agents in many organs including the liver, lung, kidney, skin and heart.

CONCLUSIONS

The main antifibrotic activity of PPARgamma agonists is to suppress the TGF-beta signaling pathway by so-called PPARgamma-dependent effect. In addition, PPARgamma agonists, especially 15d-PGJ2, also exert potentially antifibrotic activity independent of PPARgamma activation. TGF-beta1/Smads signaling not only plays many essential roles in multiple developmental processes, but also forms cross-talk networks with other signal pathways, and their inhibition by PPARgamma agonists certainly affects the cytokine networks and causes non-suspected side-effects. Anti-TGF-beta therapies with PPARgamma agonists may have to be carefully tailored to be tissue- and target gene-specific to minimize side-effects, indicating a great challenge to the medical research at present.

TGFβ1 Controls PPARγ Expression, Transcriptional Potential, and Activity, in Part, through Smad3 Signaling in Murine Lung Fibroblasts

Transforming growth factor β1 (TGFβ1) promotes fibrosis by, among other mechanisms, activating quiescent fibroblasts into myofibroblasts and increasing the expression of extracellular matrices. Recent work suggests that peroxisome proliferator-activated receptor γ (PPARγ) is a negative regulator of TGFβ1-induced fibrotic events. We, however, hypothesized that antifibrotic pathways mediated by PPARγ are influenced by TGFβ1, causing an imbalance towards fibrogenesis. Consistent with this, primary murine primary lung fibroblasts responded to TGFβ1 with a sustained downregulation of PPARγ transcripts. This effect was dampened in lung fibroblasts deficient in Smad3, a transcription factor that mediates many of the effects of TGFβ1. Paradoxically, TGFβ1 stimulated the activation of the PPARγ gene promoter and induced the phosphorylation of PPARγ in primary lung fibroblasts. The ability of TGFβ1 to modulate the transcriptional activity of PPARγ was then tested in NIH/3T3 fibroblasts containing a PPARγ-responsive luciferase reporter. In these cells, stimulation of TGFβ1 signals with a constitutively active TGFβ1 receptor transgene blunted PPARγ-dependent reporter expression induced by troglitazone, a PPARγ activator. Overexpression of PPARγ prevented TGFβ1 repression of troglitazone-induced PPARγ-dependent gene transcription, whereas coexpression of PPARγ and Smad3 transgenes recapitulated the TGFβ1 effects. We conclude that modulation of PPARγ is controlled by TGFβ1, in part through Smad3 signals, involving regulation of PPARγ expression and transcriptional potential.

Regulation of Matrix Remodeling by Peroxisome Proliferator-Activated Receptor-γ: A Novel Link Between Metabolism and Fibrogenesis

The intractable process of fibrosis underlies the pathogenesis of systemic sclerosis (SSc) and other diseases, and in aggregate contributes to 45% of deaths worldwide. Because currently there is no effective anti-fibrotic therapy, a better understanding of the pathways and cellular differentiation programs underlying fibrosis are needed. Emerging evidence points to a fundamental role of the nuclear hormone receptor peroxisome proliferator activated receptor-γ (PPAR-γ) in modulating fibrogenesis. While PPAR-γ has long been known to be important in lipid metabolism and in glucose homeostasis, its role in regulating mesenchymal cell biology and its association with pathological fibrosis had not been appreciated until recently. This article highlights recent studies revealing a consistent association of fibrosis with aberrant PPAR-γ expression and activity in various forms of human fibrosis and in rodent models, and reviews studies linking genetic manipulation of the PPAR-γ pathway in rodents and fibrosis. We survey the broad range of anti-fibrotic activities associated with PPAR-γ and the underlying mechanisms. We also summarize the emerging data linking PPAR-γ dysfunction and pulmonary arterial hypertension (PAH), which together with fibrosis is responsible for the mortality in patients in SSc. Finally, we consider current and potential future strategies for targeting PPAR-γ activity or expression as a therapy for controlling fibrosis.

Acupuncture Combined with Curcumin Attenuates Carbon Tetrachloride-Induced Hepatic Fibrosis in Rats

Background

Increasingly, studies demonstrate the effectiveness of acupuncture therapy against liver fibrosis. Curcumin is a natural product with antifibrotic effects, but has poor pharmacokinetic profiles. This study aimed to evaluate whether acupuncture combined with curcumin could more potently attenuate liver fibrosis in chemical intoxicated rats.

Methods

60 Sprague–Dawley male rats were randomly divided into control, model, sham, acupuncture, curcumin and combination therapy groups. During the establishment of fibrosis using carbon tetrachloride (CCl4), acupuncture at LR3, LR14, BL18 and ST36 and/or curcumin treatment by mouth were performed simultaneously. After treatment, pathological indexes and histology for hepatic injury and fibrogenesis were detected. The expression of extracellular matrix (ECM) components was also determined.

Results

Acupuncture combined with curcumin potently protected the liver from CCl4-induced injury and fibrogenesis, as indicated by reduced levels of serum aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, hyaluronic acid, laminin and procollagen III. Combined use also led to significant liver histological improvements. Furthermore, combined use effectively inhibited ECM expression such as α-smooth muscle actin, fibronectin and α1(1) collagen.

Conclusions

Acupuncture treatment could significantly enhance the antifibrotic efficacy of curcumin on CCl4-induced hepatic fibrosis in rats in vivo, suggesting that a combination of acupuncture with curcumin may be exploited for the prevention of hepatic fibrosis.

Peroxisome Proliferator-Activated Receptor-γ-Mediated Polarization of Macrophages in Leishmania Infection

Infection is the outcome of a contest between a pathogen and its host. In the disease leishmaniasis, the causative protozoan parasites are harbored inside the macrophages. Leishmania species adapt strategies to make the infection chronic, keeping a balance between their own and the host's defense so as to establish an environment that is favorable for survival and propagation. Activation of peroxisome proliferator-activated receptor (PPAR) is one of the tactics used. This ligand-activated nuclear factor curbs inflammation to protect the host from excessive injuries by setting a limit to its destructive force. In this paper, we report the interaction of host PPARs and the pathogen for visceral leishmaniasis, Leishmania donovani, in vivo and in vitro. PPAR expression is induced by parasitic infection. Leishmanial activation of PPARγ promotes survival, whereas blockade of PPARγ facilitates removal of the parasite. Thus, Leishmania parasites harness PPARγ to increase infectivity.

Hypoxia induces downregulation of PPAR-γ in isolated pulmonary arterial smooth muscle cells and in rat lung via transforming growth factor-β signaling

Chronic hypoxia activates transforming growth factor-β (TGF-β) signaling and leads to pulmonary vascular remodeling. Pharmacological activation of peroxisome proliferator-activated receptor-γ (PPAR-γ) has been shown to prevent hypoxia-induced pulmonary hypertension and vascular remodeling in rodent models, suggesting a vasoprotective effect of PPAR-γ under chronic hypoxic stress. This study tested the hypothesis that there is a functional interaction between TGF-β/Smad signaling pathway and PPAR-γ in isolated pulmonary artery small muscle cells (PASMCs) under hypoxic stress. We observed that chronic hypoxia led to a dramatic decrease of PPAR-γ protein expression in whole lung homogenates (rat and mouse) and hypertrophied pulmonary arteries and isolated PASMCs. Using a transgenic model of mouse with inducible overexpression of a dominant-negative mutant of TGF-β receptor type II, we demonstrated that disruption of TGF-β pathway significantly attenuated chronic hypoxia-induced downregulation of PPAR-γ in lung. Similarly, in isolated rat PASMCs, antagonism of TGF-β signaling with either a neutralizing antibody to TGF-β or the selective TGF-β receptor type I inhibitor SB431542 effectively attenuated hypoxia-induced PPAR-γ downregulation. Furthermore, we have demonstrated that TGF-β1 treatment suppressed PPAR-γ expression in PASMCs under normoxia condition. Chromatin immunoprecipitation analysis showed that TGF-β1 treatment significantly increased binding of Smad2/3, Smad4, and the transcriptional corepressor histone deacetylase 1 to the PPAR-γ promoter in PASMCs. Conversely, treatment with the PPAR-γ agonist rosiglitazone attenuated TGF-β1-induced extracellular matrix molecule expression and growth factor in PASMCs. These data provide strong evidence that activation of TGF-β/Smad signaling, via transcriptional suppression of PPAR-γ expression, mediates chronic hypoxia-induced downregulation of PPAR-γ expression in lung.

Peroxisome proliferator-activated receptor-γ cross-regulation of signaling events implicated in liver fibrogenesis

Peroxisome proliferator-activated receptor-γ (PPARγ) is a nuclear receptor with transcriptional activity controlling multiple physical and pathological processes. Recently, PPARγ has been implicated in the pathogenesis of liver fibrosis. Its depleted expression has strong associations with the activation and transdifferentiation of hepatic stellate cells, the central event in liver fibrogenesis. Studies over the past decade demonstrate that PPARγ cross-regulates a number of signaling pathways mediated by growth factors and adipokines, and cellular events including apoptosis and senescence. These signaling and cellular events and their molecular interactions with PPARγ system are profoundly involved in liver fibrogenesis. We critically summarize these mechanistic insights into the PPARγ regulation in liver fibrogenesis based on the updated findings in this area. We conclude with a discussion of the impacts of these discoveries on the interpretation of liver fibrogenesis and their potential therapeutic implications. PPARγ activation could be a promising strategy for antifibrotic therapy.

Curcumin augments lung maturation, preventing neonatal lung injury by inhibiting TGF-β signaling

There is no effective intervention to prevent or treat bronchopulmonary dysplasia (BPD). Curcumin has potent antioxidant and anti-inflammatory properties, and it modulates signaling of peroxisome proliferator-activated receptor-γ (PPARγ), an important molecule in the pathobiology of BPD. However, its role in the prevention of BPD is not known. We determined 1) if curcumin enhances neonatal lung maturation, 2) if curcumin protects against hyperoxia-induced neonatal lung injury, and 3) if this protection is mediated by blocking TGF-β. Embryonic day 19 fetal rat lung fibroblasts were exposed to 21% or 95% O(2) for 24 h following 1 h of treatment with curcumin. Curcumin dose dependently accelerated e19 fibroblast differentiation [increased parathyroid hormone-related protein (PTHrP) receptor, PPARγ, and adipocyte differentiation-related protein (ADRP) levels and triolein uptake] and proliferation (increased thymidine incorporation). Pretreatment with curcumin blocked the hyperoxia-induced decrease (PPARγ and ADRP) and increase (α-smooth muscle actin and fibronectin) in markers of lung injury/repair, as well as the activation of TGF-β signaling. In a separate set of experiments, neonatal Sprague-Dawley rat pups were exposed to 21% or 95% O(2) for 7 days with or without intraperitoneal administration of curcumin. Analysis for markers of lung injury/repair [PTHrP receptor, PPARγ, ADRP, fibronectin, TGF-β receptor (activin receptor-like kinase 5), and Smad3] and lung morphology (radial alveolar count) demonstrated that curcumin effectively blocks TGF-β activation and hyperoxia-induced lung injury. Therefore, curcumin accelerates lung maturation by stimulating key alveolar epithelial-mesenchymal interactions and prevents hyperoxia-induced neonatal lung injury, possibly by blocking TGF-β activation, suggesting that it is a potential intervention against BPD.

A Novel Mechanism of PPARgamma Regulation of TGFbeta1: Implication in Cancer Biology

Peroxisome proliferator-activated receptor-γ (PPARγ) and retinoic acid X-receptor (RXR) heterodimer, which regulates cell growth and differentiation, represses the TGFβ1 gene that encodes for the protein involved in cancer biology. This review will introduce the novel mechanism associated with the inhibition of the TGFβ1 gene by PPARγ activation, which regulates the dephosphorylation of Zf9 transcription factor. Pharmacological manipulation of TGFβ1 by PPARγ activators can be applied for treating TGFβ1-induced pathophysiologic disorders such as cancer metastasis and fibrosis. In this article, we will discuss the opposing effects of TGFβ on tumor growth and metastasis, and address the signaling pathways regulated by PPARγ for tumor progression and suppression.

PPARγ downregulation by TGFß in fibroblast and impaired expression and function in systemic sclerosis: a novel mechanism for progressive fibrogenesis

The nuclear orphan receptor peroxisome proliferator-activated receptor-gamma (PPAR-γ) is expressed in multiple cell types in addition to adipocytes. Upon its activation by natural ligands such as fatty acids and eicosanoids, or by synthetic agonists such as rosiglitazone, PPAR-γ regulates adipogenesis, glucose uptake and inflammatory responses. Recent studies establish a novel role for PPAR-γ signaling as an endogenous mechanism for regulating transforming growth factor-ß (TGF-ß)-dependent fibrogenesis. Here, we sought to characterize PPAR-γ function in the prototypic fibrosing disorder systemic sclerosis (SSc), and delineate the factors governing PPAR-γ expression. We report that PPAR-γ levels were markedly diminished in skin and lung biopsies from patients with SSc, and in fibroblasts explanted from the lesional skin. In normal fibroblasts, treatment with TGF-ß resulted in a time- and dose-dependent down-regulation of PPAR-γ expression. Inhibition occurred at the transcriptional level and was mediated via canonical Smad signal transduction. Genome-wide expression profiling of SSc skin biopsies revealed a marked attenuation of PPAR-γ levels and transcriptional activity in a subset of patients with diffuse cutaneous SSc, which was correlated with the presence of a "TGF-ß responsive gene signature" in these biopsies. Together, these results demonstrate that the expression and function of PPAR-γ are impaired in SSc, and reveal the existence of a reciprocal inhibitory cross-talk between TGF-ß activation and PPAR-γ signaling in the context of fibrogenesis. In light of the potent anti-fibrotic effects attributed to PPAR-γ, these observations lead us to propose that excessive TGF-ß activity in SSc accounts for impaired PPAR-γ function, which in turn contributes to unchecked fibroblast activation and progressive fibrosis.

Methylated chrysin, a dimethoxy flavone, partially suppresses the development of liver preneoplastic lesions induced by N-nitrosodiethylamine in rats

The modifying effect of chemically modified chrysin on formation of preneoplastic foci induced by N-nitrosodiethylamine (DEN) was investigated in male rats. Male Wistar rats were administered three intraperitoneal injections of DEN (200 mg/kg bodyweight) interspersed by 2 weeks with or without an oral dose of dimethoxy flavone (DMF 100 mg/kg bodyweight), 2 weeks after DEN initiation. The number of GST-Pi positive foci and proliferating cell nuclear antigen (PCNA)-positive cells were significantly suppressed by the administration of DMF. Real-time RT-PCR analysis revealed that DMF treatment increased mRNA expression levels of apoptotic proteins p53 and fas, cell cycle regulatory proteins chek 2, cdkn1a, rad 50, anti-inflammatory protein pparg whereas the mRNA expression levels of bcl-2 and prdx-2 were decreased compared to mRNA levels in DEN-treated group. Therefore, we propose that DMF partially suppresses the formation of preneoplastic lesions in rats following DEN exposure by regulating anti-inflammatory and apoptosis-promoting events and restoring the cellular redox balance altered by DEN.

Curcumin inhibits fibrosis-related effects in IPF fibroblasts and in mice following bleomycin-induced lung injury

Idiopathic pulmonary fibrosis (IPF) is a progressive and typically fatal lung disease for which no effective therapy has been identified. The disease is characterized by excessive collagen deposition, possibly in response to dysregulated wound healing. Mediators normally involved in would healing induce proliferation of fibroblasts and their differentiation to myofibroblasts that actively secrete collagen. Curcumin, a polyphenolic compound from turmeric, has been shown to exert a variety of biological effects. Effects on IPF and associated cell types remain unclear, however. We accordingly tested the ability of curcumin to inhibit proliferation and differentiation to myofibroblasts by human lung fibroblasts, including those from IPF patients. To further examine the potential usefulness of curcumin in IPF, we examined its ability to reduce fibrosis in bleomycin-treated mice. We show that curcumin effectively reduces profibrotic effects in both normal and IPF fibroblasts in vitro and that this reduction is accompanied by inhibition of key steps in the transforming growth factor-β (TGF-β) signaling pathway. In vivo, oral curcumin treatment showed no effect on important measures of bleomycin-induced injury in mice, whereas intraperitoneal curcumin administration effectively inhibited inflammation and collagen deposition along with a trend toward improved survival. Intraperitoneal curcumin reduced fibrotic progression even when administered after the acute bleomycin-induced inflammation had subsided. These results encourage further research on alternative formulations and routes of administration for this potentially attractive IPF therapy.

Curcumin limits the fibrogenic evolution of experimental steatohepatitis

Nonalcoholic steatohepatitis is characterized by the association of steatosis with hepatic cell injury, lobular inflammation and fibrosis. Curcumin is known for its antioxidant, anti-inflammatory and antifibrotic properties. The aim of this study was to test whether the administration of curcumin limits fibrogenic evolution in a murine model of nonalcoholic steatohepatitis. Male C57BL/6 mice were divided into four groups and fed a diet deficient in methionine and choline (MCD) or the same diet supplemented with methionine and choline for as long as 10 weeks. Curcumin (25 microg per mouse) or its vehicle (DMSO) was administered intraperitoneally every other day. Fibrosis was assessed by Sirius red staining and histomorphometry. Intrahepatic gene expression was measured by quantitative PCR. Hepatic oxidative stress was evaluated by staining for 8-OH deoxyguanosine. Myofibroblastic hepatic stellate cells (HSCs) were isolated from normal human liver tissue. The increase in serum ALT caused by the MCD diet was significantly reduced by curcumin after 4 weeks. Administration of the MCD diet was associated with histological steatosis and necro-inflammation, and this latter was significantly reduced in mice receiving curcumin. Curcumin also inhibited the generation of hepatic oxidative stress. Fibrosis was evident after 8 or 10 weeks of MCD diet and was also significantly reduced by curcumin. Curcumin decreased the intrahepatic gene expression of monocyte chemoattractant protein-1, CD11b, procollagen type I and tissue inhibitor of metalloprotease (TIMP)-1, together with protein levels of alpha-smooth muscle-actin, a marker of fibrogenic cells. In addition, curcumin reduced the generation of reactive oxygen species in cultured HSCs and inhibited the secretion of TIMP-1 both in basal conditions and after the induction of oxidative stress. In conclusion, curcumin administration effectively limits the development and progression of fibrosis in mice with experimental steatohepatitis, and reduces TIMP-1 secretion and oxidative stress in cultured stellate cells.

Curcumin attenuates the effects of insulin on stimulating hepatic stellate cell activation by interrupting insulin signaling and attenuating oxidative stress

Hyperinsulinemia associated with type II diabetes mellitus (T2DM) is a risk factor for non-alcoholic steatohepatitis (NASH) and hepatic fibrosis. Hepatic stellate cells (HSCs) are the major effectors in collagen production during hepatic fibrogenesis. Elevated levels of insulin stimulate HSC activation. In addition to its anti-diabetic effects, the antioxidant curcumin, the yellow pigment in curry from turmeric, suppresses HSC activation and protects the liver from fibrogenesis in vitro and in vivo. This study aims at evaluating the effect of curcumin on insulin-induced HSC activation and further elucidating the underlying mechanisms. We report that curcumin dose-dependently eliminates insulin-induced HSC activation by suppressing expression of type I collagen gene and other key genes relevant to HSC activation. Additional experiments indicate that curcumin interrupts insulin signaling in HSCs by reducing the phosphorylation level of insulin receptor (InsR) and suppressing gene expression of InsR. Furthermore, curcumin attenuates insulin-induced oxidative stress in HSCs by inducing gene expression of glutamate-cysteine ligase (GCL), leading to de novo synthesis of glutathione and the suppression of gene expression of InsR. These results support our initial hypothesis that curcumin inhibits the effects of insulin on stimulating HSC activation by interrupting insulin signaling and attenuating oxidative stress. Our results provide novel insights into the mechanisms by which curcumin inhibits the insulin-induced HSC activation.