Effects of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) on the expression of inflammatory cytokines and apoptosis induction in rheumatoid synovial fibroblasts and monocytes

PPARs in Clinical Experimental Medicine after 35 Years of Worldwide Scientific Investigations and Medical Experiments

This year marks the 35th anniversary of Professor Walter Wahli's discovery of the PPARs (Peroxisome Proliferator-Activated Receptors) family of nuclear hormone receptors. To mark the occasion, the editors of the scientific periodical Biomolecules decided to publish a special issue in his honor. This paper summarizes what is known about PPARs and shows how trends have changed and how research on PPARs has evolved. The article also highlights the importance of PPARs and what role they play in various diseases and ailments. The paper is in a mixed form; essentially it is a review article, but it has been enriched with the results of our experiments. The selection of works was subjective, as there are more than 200,000 publications in the PubMed database alone. First, all papers done on an animal model were discarded at the outset. What remained was still far too large to describe directly. Therefore, only papers that were outstanding, groundbreaking, or simply interesting were described and briefly commented on.

Mechanisms and functions of SUMOylation in health and disease: a review focusing on immune cells

SUMOylation, which is a type of post-translational modification that involves covalent conjugation of small ubiquitin-like modifier (SUMO) proteins to target substrates, regulates various important molecular and cellular processes, including transcription, the cell cycle, cell signaling, and DNA synthesis and repair. Newly synthesized SUMO is immature and cleaved by the SUMO-specific protease family, resulting in exposure of the C-terminal Gly-Gly motif to become the mature form. In the presence of ATP, mature SUMO is conjugated with the activating enzyme E1 through the cysteine residue of E1, followed by transfer to the cysteine residue of E2-conjugating enzyme Ubc9 in humans that recognizes and modifies the lysine residue of a substrate protein. E3 SUMO ligases promote SUMOylation. SUMOylation is a reversible modification and mediated by SUMO-specific proteases. Cumulative studies have indicated that SUMOylation affects the functions of protein substrates in various manners, including cellular localization and protein stability. Gene knockout studies in mice have revealed that several SUMO cycling machinery proteins are crucial for the development and differentiation of various cell lineages, including immune cells. Aberrant SUMOylation has been implicated in several types of diseases, including cancers, cardiovascular diseases, and autoimmune diseases. This review summarizes the biochemistry of SUMO modification and the general biological functions of proteins involved in SUMOylation. In particular, this review focuses on the molecular mechanisms by which SUMOylation regulates the development, maturation, and functions of immune cells, including T, B, dendritic, and myeloid cells. This review also discusses the underlying relevance of disruption of SUMO cycling and site-specific interruption of SUMOylation on target proteins in immune cells in diseases, including cancers and infectious diseases.

The SUMO components in rheumatoid arthritis

Small ubiquitin-like modifier (SUMO) proteins can reversibly attach covalently or non-covalently to lysine residues of various substrates. The processes are named SUMOylation and de-SUMOylation, which maintain a dynamic balance in the physiological state, and are regulated by SUMO components. However, the dysregulation of components disturbs the balance and alters the functions of target proteins, which causes the occurrence of diseases. To date, certain SUMO components, including SUMO-1, SUMO-2/3, SAE1/Uba2, Ubc9, PIASs (protein inhibitors of activated signal transducer and activator of transcription) and SENPs (SUMO-specific proteases), have been found to participate in the pathogenesis of RA and their potential value as therapeutic targets also have been highlighted. In addition, single nucleotide polymorphisms (SNPs) in the SUMO components have been reported to be associated with disease susceptibility. Until now, only the SNP site of SUMO-4 has been reported in RA. Here we provided a systematic overview of the general characteristics of SUMO components and highlighted a summary of their impact on RA.

Arisaema heterophyllum Blume Monomer Stigmasterol Targets PPARγ and Inhibits the Viability and Tumorigenicity of Lung Adenocarcinoma Cells NCI-H1975

To clarify the regulatory effect and molecular mechanism of Arisaema heterophyllum Blume (AhBl) monomer stigmasterol on lung adenocarcinoma in human lung adenocarcinoma cells NCI-H1975 cultured in vitro and in nude mice. Oil red O staining, free fatty acid detection, adenosine triphosphate (ATP), and NADPH were applied to elucidate the regulatory effect of stigmasterol on the energy metabolism of NCI-H1975 cells. Simultaneously, colony formation assay and nude mouse tumorigenesis were performed to clarify the underlying mechanisms of stigmasterol on the proliferation and tumorigenesis of NCI-H1975 cells. Furthermore, peroxisome proliferator-activated receptor gamma (PPARγ) inhibitor GW9662 was supplemented to determine the expression changes of cyclins to clarify the regulation mechanism of stigmasterol. The results revealed that stigmasterol administration markedly inhibited the viability but promoted lipid deposition of NCI-H1975 cells. Meanwhile, the reduction of cell energy metabolism affected cell proliferation and colony formation. qPCR and western blot assays indicated that stigmasterol played a role in regulating the expression of cyclins and PPARγ signaling pathway proteins. Nude mouse tumorigenesis suggested that tumor size and weight in the stigmasterol-treated group were apparently lower as compared with the control group. Tumor tissue cells developed varying degrees of degeneration and large areas of ischemic necrosis presented in the central and peripheral cells. Immunohistochemistry results revealed that Ki67 expression in the stigmasterol group was substantially inhibited, while PPARγ expression was greatly elevated as compared with the control. GW9662 could mediate the inhibitory effect of stigmasterol on NCI-H1975 cells. The current study demonstrated that stigmasterol targeted PPARγ and inhibited the viability and tumorigenicity of lung adenocarcinoma cells NCI-H1975.

Fatty Acid Fingerprints and Hyaluronic Acid in Extracellular Vesicles from Proliferating Human Fibroblast-like Synoviocytes

Extracellular vesicles (EVs) function as conveyors of fatty acids (FAs) and other bioactive lipids and can modulate the gene expression and behavior of target cells. EV lipid composition influences the fluidity and stability of EV membranes and reflects the availability of lipid mediator precursors. Fibroblast-like synoviocytes (FLSs) secrete EVs that transport hyaluronic acid (HA). FLSs play a central role in inflammation, pannus formation, and cartilage degradation in joint diseases, and EVs have recently emerged as potential mediators of these effects. The aim of the present study was to follow temporal changes in HA and EV secretion by normal FLSs, and to characterize the FA profiles of FLSs and EVs during proliferation. The methods used included nanoparticle tracking analysis, confocal laser scanning microscopy, sandwich-type enzyme-linked sorbent assay, quantitative PCR, and gas chromatography. The expression of hyaluronan synthases 1-3 in FLSs and HA concentrations in conditioned media decreased during cell proliferation. This was associated with elevated proportions of 20:4n-6 and total n-6 polyunsaturated FAs (PUFAs) in high-density cells, reductions in n-3/n-6 PUFA ratios, and up-regulation of cluster of differentiation 44, tumor necrosis factor α, peroxisome proliferator-activated receptor (PPAR)-α, and PPAR-γ. Compared to the parent FLSs, 16:0, 18:0, and 18:1n-9 were enriched in the EV fraction. EV counts decreased during cell growth, and 18:2n-6 in EVs correlated with the cell count. To conclude, FLS proliferation was featured by increased 20:4n-6 proportions and reduced n-3/n-6 PUFA ratios, and FAs with a low degree of unsaturation were selectively transferred from FLSs into EVs. These FA modifications have the potential to affect membrane fluidity, biosynthesis of lipid mediators, and inflammatory processes in joints, and could eventually provide tools for translational studies to counteract cartilage degradation in inflammatory joint diseases.

Anti-inflammatory and modulatory effects of steroidal saponins and sapogenins on cytokines: A review of pre-clinical research

BACKGROUND

Saponins are glycosides which, after acid hydrolysis, liberate sugar(s) and an aglycone (sapogenin) which can be triterpenoid or steroidal in nature. Steroidal saponins and sapogenins have attracted significant attention as important natural anti-inflammatory compounds capable of acting on the activity of several inflammatory cytokines in various inflammatory models.

PURPOSE

The aim of this review is to collect preclinical in vivo studies on the anti-inflammatory activity of steroidal saponins through the modulation of inflammatory cytokines.

STUDY DESIGN AND METHODS

This review was carried out through a specialized search in three databases, that were accessed between September and October, 2021, and the publication period of the articles was not limited. Information about the name of the steroidal saponins, the animals used, the dose and route of administration, the model of pain or inflammation used, the tissue and experimental method used in the measurement of the cytokines, and the results observed on the levels of cytokines was retrieved.

RESULTS

Forty-five (45) articles met the inclusion criteria, involving the saponins cantalasaponin-1, α-chaconine, dioscin, DT-13, lycoperoside H, protodioscin, α-solanine, timosaponin AIII and BII, trillin, and the sapogenins diosgenin, hecogenin, and ruscogenin. The surveys were carried out in seven different countries and only articles between 2007 and 2021 were found. The studies included in the review showed that the saponins and sapogenins were anti-inflammatory, antinociceptive and antioxidant and they modulate inflammatory cytokines mainly through the Nf-κB, TLR4 and MAPKs pathways.

CONCLUSION

Steroidal saponins and sapogenins are promising compounds in handling of pain and inflammation for the development of natural product-derived drugs. However, it is necessary to increase the methodological quality of preclinical studies, mainly blinding and sample size calculation.

Relevance of Peroxisome Proliferator Activated Receptors in Multitarget Paradigm Associated with the Endocannabinoid System

Cannabinoids have shown to exert their therapeutic actions through a variety of targets. These include not only the canonical cannabinoid receptors CB1R and CB2R but also related orphan G protein-coupled receptors (GPCRs), ligand-gated ion channels, transient receptor potential (TRP) channels, metabolic enzymes, and nuclear receptors. In this review, we aim to summarize reported compounds exhibiting their therapeutic effects upon the modulation of CB1R and/or CB2R and the nuclear peroxisome proliferator-activated receptors (PPARs). Concomitant actions at CBRs and PPARα or PPARγ subtypes have shown to mediate antiobesity, analgesic, antitumoral, or neuroprotective properties of a variety of phytogenic, endogenous, and synthetic cannabinoids. The relevance of this multitargeting mechanism of action has been analyzed in the context of diverse pathologies. Synergistic effects triggered by combinatorial treatment with ligands that modulate the aforementioned targets have also been considered. This literature overview provides structural and pharmacological insights for the further development of dual cannabinoids for specific disorders.

Fortified vegetarian milk for prevention of metabolic syndrome in rats: impact on hepatic and vascular complications

Metabolic syndrome (MetS) is characterized as a gathering of various metabolic disorders, for example, hyperglycemia, dyslipidemia, and obesity. The present research was conducted to prepare fortified almond milk as functional beverages and evaluate their protective effect against MetS and associated hepatic and vascular complications. Three beverages (I, II, and III) were prepared by fortification almond milk with carrot juice or powder of quinoa seeds and carrot juice or oat powder and banana juice. The sensory attributes, physicochemical properties, bioactive compounds (total phenolic, beta-carotene, tocopherols) and B-complex vitamins were determined in the beverages. In-vitro antioxidant activity of the beverages was assessed. MetS was induced in rats via feeding on high-fat high-fructose diet (HFHF). The biochemical (lipid profile, oxidative stress, liver, and kidney functions), nutritional and histopathological parameters were assessed in rats. The beverage I recorded the highest sensory attributes' scores. The physicochemical properties of the beverages revealed that acidity and viscosity of all beverages ranged from 4.55 to 4.88 and from 40 to 59, respectively. The beverage I showed the highest content of alpha-tocopherol (14.994 μg/g) and beta-carotene (104.541 μg/g), while the beverage II showed the highest content of gamma-tocopherol (0.557 μg/g), folic acid (0.806 μg/g), and total phenols (147.43 μg GAE/g). The results of animals revealed that the beverage II was the most promising in attenuation levels of total cholesterol, triglycerides, low-density lipoprotein cholesterol, malondialdehyde, and tumor necrosis factor-alpha. Also, the beverage II was the superior in the protection of the liver and heart tissues as reflected by the histopathological examination findings. So, it can be concluded that the newly prepared almond milk with quinoa seeds and carrot juice could be used as an effective functional beverage for the prevention of MetS and its complications.

Heme Oxygenase-1 Upregulation: A Novel Approach in the Treatment of Cardiovascular Disease

Significance: Heme oxygenase (HO) plays a pivotal role in both vascular and metabolic functions and is involved in many physiological and pathophysiological processes in vascular endothelial cells (ECs) and adipocytes. Recent Advances: From the regulation of adipogenesis in adipose tissue to the adaptive response of vascular tissue in the ECs, HO plays a critical role in the capability of the vascular system to respond and adjust to insults in homeostasis. Recent studies show that HO-1 through regulation of adipocyte and adipose tissue functions ultimately aid not only in local but also in systemic maintenance of homeostasis. Critical Issues: Recent advances have revealed the existence of a cross talk between vascular ECs and adipocytes in adipose tissue. In the pathological state of obesity, this cross talk contributes to the condition's adverse chronic effects, and we propose that specific targeting of the HO-1 gene can restore signaling pathways and improve both vascular and adipose functions. Future Directions: A complete understanding of the role of HO-1 in regulation of cardiovascular homeostasis is important to comprehend the homeostatic regulation as well as in cardiovascular disease. Efforts are required to highlight the effects and the ability to target the HO-1 gene in models of obesity with an emphasis on the role of pericardial fat on cardiovascular health.

Bis(ethylmaltolato)oxidovanadium (IV) mitigates neuronal apoptosis resulted from amyloid-beta induced endoplasmic reticulum stress through activating peroxisome proliferator-activated receptor γ

Neuronal apoptosis caused by amyloid-beta (Aβ) overproduction is one of the most important pathological features in Alzheimer's disease (AD). Endoplasmic reticulum (ER) stress induced by Aβ overload plays a critical role in this process. Bis(ethylmaltolato)oxidovanadium (IV) (BEOV), a vanadium compound which had been regarded as peroxisome proliferator-activated receptor γ (PPARγ) agonist, was reported to exert an antagonistic effect on ER stress. In this study, we tested whether BEOV could ameliorate the Aβ-induced neuronal apoptosis by inhibiting ER stress. It was observed that BEOV treatment ameliorated both tunicamycin-induced and/or Aβ-induced ER stress and neurotoxicity in a dose-dependent manner through downgrading ER stress-associated and apoptosis-associated proteins in primary hippocampal neurons. Consistent with in vitro results, BEOV also reduced ER stress and inhibited neuronal apoptosis in hippocampi and cortexes of transgenic AD model mice. Moreover, by adopting GW9662 and salubrinal, the inhibitor of PPARγ and hyperphosphorylated eukaryotic translation initiation factor 2α, respectively, we further confirmed that BEOV alleviated Aβ-induced ER stress and neuronal apoptosis in primary hippocampal neurons by activating PPARγ. Taken together, these results provided scientific evidences to support the concept that BEOV ameliorates Aβ-induced ER stress and neuronal apoptosis through activating PPARγ.

A locked immunometabolic switch underlies TREM2 R47H loss of function in human iPSC-derived microglia

Loss‐of‐function genetic variants of triggering receptor expressed on myeloid cells 2 (TREM2) are linked with an enhanced risk of developing dementias. Microglia, the resident immune cell of the brain, express TREM2, and microglial responses are implicated in dementia pathways. In a normal surveillance state, microglia use oxidative phosphorylation for their energy supply, but rely on the ability to undergo a metabolic switch to glycolysis to allow them to perform rapid plastic responses. We investigated the role of TREM2 on the microglial metabolic function in human patient iPSC‐derived microglia expressing loss of function variants in TREM2. We show that these TREM2 variant iPSC‐microglia, including the Alzheimer's disease R47H risk variant, exhibit significant metabolic deficits including a reduced mitochondrial respiratory capacity and an inability to perform a glycolytic immunometabolic switch. We determined that dysregulated PPARγ/p38MAPK signaling underlies the observed phenotypic deficits in TREM2 variants and that activation of these pathways can ameliorate the metabolic deficit in these cells and consequently rescue critical microglial cellular function such as β‐Amyloid phagocytosis. These findings have ramifications for microglial focussed‐treatments in AD.

Positive Effects of Heme Oxygenase Upregulation on Adiposity and Vascular Dysfunction: Gene Targeting vs. Pharmacologic Therapy

Objective: Heme oxygenase (HO-1) plays a critical role in adipogenesis and it is important to understand its function in obesity. Many studies have shown that upregulation of HO-1 can affect the biologic parameters in obesity-mediated diabetes, hypertension and vascular endothelial cell function. Thus, we aimed to explore the hypothesis that upregulation of HO-1, using a pharmacologic approach as well as gene targeting, would improve both adiposity and endothelial cell dysfunction by direct targeting of endothelial cells. Our second aim was to compare the short-term effect of a HO-1 inducer, cobalt-protoporphrin IX (CoPP), with the long-term effects of gene targeted therapy on vascular and adipocyte stem cells in obese mice. Method: We examined the effect of CoPP on fat pre-adipocytes and mesenchymal stem cells (MSC) in mice fed a high-fat diet (HFD). We also used a lentiviral construct that expressed heme oxygenase (HO-1) that was under the control of an endothelium specific promoter, vascular endothelium cadherin (VECAD) heme oxygenase (VECAD-HO-1). We targeted endothelial cells using vascular endothelium cadherin/green fluorescent protein fusion construct (VECAD-GFP) as the control. Conditioned media (CM) from endothelial cells (EC) was added to fat derived adipocytes. Additionally, we treated renal interlobar arteries with phenylephrine and dosed cumulative increments of acetylcholine both with and without exposure to CoPP. We did the same vascular reactivity experiments with VECAD-HO-1 lentiviral construct compared to the control. Results: CoPP improved vascular reactivity and decreased adipogenesis compared to the control. MSCs exposed to CM from EC transfected with VECAD-HO-1 showed decreased adipogenesis, smaller lipid droplet size and decreased PPAR-γ, C/EBP and increased Wnt 10b compared to the control. HO-1 upregulation had a direct effect on reducing adipogenesis. This effect was blocked by tin mesoporphrin (SnMP). EC treated with VECAD-HO-1 expressed lower levels of ICAM and VCAM compared to the control, suggesting improved EC function. This also improved ACH induced vascular reactivity. These effects were also reversed by SnMP. The effect of viral transfection was much more specific and sustained than the effects of pharmacologic therapy, CoPP. Conclusion: This study demonstrates that a pharmacological inducer of HO-1 such as CoPP improves endothelial cell function while dampening adipogenesis, but long-term HO-1 expression by direct targeting of endothelial cells by gene transfer therapy may offer a more specific and ideal solution. This was evidenced by smaller healthier adipocytes that had improved insulin sensitivity, suggesting increased adiponectin levels. HO-1 upregulation reestablished the “crosstalk” between perivascular adipose tissue and the vascular system that was lost in the chronic inflammatory state of obesity. This study demonstrates that gene targeting of EC may well be the future direction in treating obesity induced EC dysfunction, with the finding that targeting the vasculature had a direct and sustained effect on adipogenesis.

Oridonin inhibits IL-1β-induced inflammation in human osteoarthritis chondrocytes by activating PPAR-γ

Osteoarthritis (OA), a progressive disease of the joints, affects millions of people worldwide. In the present study, we investigated the effects of oridonin, a diterpenoid isolated from Rabdosia rubescens, on IL-1β-induced inflammation using human osteoarthritis chondrocytes. The results showed that oridonin significantly suppressed IL-1β-induced MMP1, MMP3, and MMP13 production. IL-1β-induced NO and PGE₂ production, as well as inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression were also attenuated by oridonin. Western blot analysis demonstrated IL-1β-induced NF-κB activation was reduced by oridonin. Furthermore, the expression of PPAR-γ was increased by oridonin in a concentration-dependent manner. PPAR-γ antagonist could reverse the anti-inflammatory activity of oridonin. The results suggested that oridonin could be a candidate agent for the treatment of OA.

A cytokine protein-protein interaction network for identifying key molecules in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease of the synovial joints. Though the current RA therapeutics such as disease-modifying antirheumatic drugs (DMARDs), nonsteroidal anti-inflammatory drugs (NSAIDs) and biologics can halt the progression of the disease, none of these would either dramatically reduce or cure RA. So, the identification of potential therapeutic targets and new therapies for RA are active areas of research. Several studies have discovered the involvement of cytokines in the pathogenesis of this disease. These cytokines induce signal transduction pathways in RA synovial fibroblasts (RASF). These pathways share many signal transducers and their interacting proteins, resulting in the formation of a signaling network. In order to understand the involvement of this network in RA pathogenesis, it is essential to identify the key transducers and their interacting proteins that are part of this network. In this study, based on a detailed literature survey, we have identified a list of 12 cytokines that induce signal transduction pathways in RASF. For these cytokines, we have built a signaling network using the protein-protein interaction (PPI) data that was obtained from public repositories such as HPRD, BioGRID, MINT, IntAct and STRING. By combining the network centrality measures with the gene expression data from the RA related microarrays that are available in the open source Gene Expression Omnibus (GEO) database, we have identified 24 key proteins of this signaling network. Two of these 24 are already drug targets for RA, and of the remaining, 12 have direct PPI links to some of the current drug targets of RA. Therefore, these key proteins seem to be crucial in the pathogenesis of RA and hence might be treated as potential drug targets.

Ginsenoside Rg1 attenuates adjuvant-induced arthritis in rats via modulation of PPAR-γ/NF-κB signal pathway

Ginsenoside Rg1, the main active compound in Panax ginseng, has already been shown to have anti-inflammatory effects. However, the protective effects of Rg1 on rheumatoid arthritis (RA) remain unclear. The aim of the present study was to investigate the effects and mechanisms of Rg1 on adjuvant-induced arthritis (AIA) in rats. AIA rats were given Rg1 at doses of 5, 10, and 20 mg/kg intraperitoneally for 14 days to observe the anti-arthritic effects. The results showed that Rg1 significantly alleviated joint swelling and injuries. Rg1 can also significantly reduce the level of TNF-α and IL-6, increase PPAR-γ protein expression, inhibit IκBα phosphorylation and NF-κB nuclear translocation in the inflammatory joints of AIA rats and RAW264.7 cells stimulated by lipopolysaccharide (LPS). The results indicate that Rg1 has therapeutic effects on AIA rats, and the mechanism might be associated with its anti-inflammatory effects by up-regulating PPAR-γ and subsequent inhibition of NF-κB signal pathway.

Troglitazone, a PPAR-γ agonist, decreases LTC4 concentration in mononuclear cells in patients with asthma

BACKGROUND

Asthma is an inflammatory disorder with multiple mediators involved in the inflammatory response. Despite several attempts, no new anti-inflammatory drugs have been registered for asthma treatment for several years. However, thiazolidinediones, peroxisome proliferator-activated receptor agonists, have demonstrated some anti-inflammatory properties in various experimental settings. The aim of this study was to assess the influence of troglitazone on LTC₄ and 15-HETE concentrations. It also evaluates TNF-induced eotaxin synthesis in peripheral blood mononuclear cells from 14 patients with mild asthma and 13 healthy controls.

METHODS

PBMCs were isolated from the whole blood of the asthmatics and healthy subjects and pretreated with 0.1, 1 or 10μM of Troglitazone. The cells were then exposed to 10^-6M calcium jonophore or 10ng/ml TNF. The production and release of LTC₄, 15-HETE and eotaxin were then assessed.

RESULTS

Troglitazone caused a dose-dependent inhibition in LTC₄ synthesis in both asthmatics and healthy subjects. Troglitazone did not influence 15-HETE or eotaxin production in either asthmatic patients or in healthy individuals.

CONCLUSION

Due to its inhibition of LTC₄ synthesis, troglitazone therapy is an interesting potential therapeutic approach in asthma and other LTC₄ related inflammatory disorders.

PPARγ agonist rosiglitazone inhibits migration and invasion by downregulating Cyr61 in rheumatoid arthritis fibroblast-like synoviocytes

AIM

Peroxisome proliferator-activated receptor gamma (PPARγ) agonists have anti-inflammatory properties that reduce inflammatory cytokine production in rheumatoid arthritis (RA). Cysteine-rich angiogenic inducer 61 (Cyr61) is associated with diseases related to chronic inflammation. The aim of this study was to investigate the mechanisms underlying the effects of PPARγ agonists on tumor necrosis factor (TNF)-α-induced fibroblast-like synoviocyte (FLS) invasion and migration, as well as Cyr61 production, in RA-FLS.

METHODS

FLS were cultured with TNF-α and Cyr61 in the presence or absence of PPARγ agonists. Matrix metalloproteinase and Cyr61 expression levels in RA-FLS and culture supernatants were measured by reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting. The migration and invasion phenotypes of RA-FLS were determined by wound healing and Boyden chamber assays.

RESULTS

Cyr61 protein was expressed in RA-FLS, and its intracellular expression and secretion levels were increased by TNF-α. Moreover, Cyr61 directly promoted RA-FLS migration and invasion. Rosiglitazone (RSG) significantly decreased TNF-α-induced Cyr61 expression. RSG decreased TNF-α-induced nuclear factor (NF)-κB activation and inhibitor of κBα degradation. Furthermore, RSG inhibited TNF-α-induced RA-FLS migration and invasion and decreased Cyr61 treatment-induced RA-FLS invasion. Finally, blocking Cyr61 significantly attenuated TNF-α-induced migration.

CONCLUSIONS

Our results demonstrate for the first time that PPARγ agonists may have beneficial effects on the migration and invasion of RA-FLS via the downregulation of Cyr61. Therefore, PPARγ agonists could be potential treatment targets for RA.

Multitargeted bioactive ligands for PPARs discovered in the last decade

Type 2 diabetes took insulin resistance as the main clinical manifestation. PPARs have been reported to be the therapeutic targets of metabolic disorders, such as obesity, hypertension, diabetes, and cardiovascular disease. Previously, PPARγ agonist rosiglitazone was restricted in clinic due to cardiomyocytes infarction, weight gain, and other serious side-effects, which were mainly due to the single and selective PPARγ agonism. In recent years, multitarget-directed PPAR agonists with synergistic reaction as well as fewer side-effect have been the hot topic in designing promising agents. In this review, we updated and generalized the development of PPARγ partial agonists, PPARγ antagonists, PPARα/γ dual agonists, PPARδ partial agonists, PPARδ antagonists, PPARα/δ dual agonists, PPARγ/δ dual agonists, and PPARα/γ/δ pan-agonists published in recent decade. Most of these molecules were modified from known structures or came from high-throughput screening. Among these molecules, some were expected to be promising drugs against metabolic disorders, while others seemed to provide new insight for designing novel PPAR agents.

Establishment of a rabbit model to study the influence of advanced glycation end products accumulation on osteoarthritis and the protective effect of pioglitazone

OBJECTIVE

To investigate the role of advanced glycation end products (AGEs) in cartilage degeneration in vivo and determine the influence of the peroxisome proliferator-activated receptor-γ (PPARγ) agonist pioglitazone on AGEs-induced osteoarthritis (OA) in a rabbit model.

DESIGN

Thirty-two rabbits were separated into four groups (n = 8 each) and received 500 μL of 123, 350, or 1000 mmol/L D-ribose or Phosphate buffered saline (PBS) solution administered to the right stifle joint via intra-articular injection twice a week. All the rabbits ran 500 m on treadmills every day. Another 16 rabbits were administered 1000 mmol/L D-ribose and divided into 2 groups (n = 8) that received either placebo or pioglitazone administered orally at 20 mg/kg/day. Eight weeks later, cartilage damage was evaluated macroscopically, histologically, and biochemically.

RESULTS

Artificially increasing the AGEs level and exercise load resulted in cartilage damage and dose-dependent downregulation of PPARγ expression. The efficacy of pioglitazone treatment was tested in a rabbit OA model, and a clear chondroprotective effect was revealed by macro- and microscopic assessments.

CONCLUSION

Elevating AGEs in rabbits can accelerate the articular cartilage degradation that occurs with physical exercise, and pioglitazone can reduce the severity of the AGEs-induced OA in a rabbit model.

Metabolic stress-induced joint inflammation and osteoarthritis

Osteoarthritis (OA) is a heterogeneous disorder with several risk factors. Among them, obesity has a major impact on both loading and non-loading joints. Mechanical overload and activity of systemic inflammatory mediators derived from adipose tissue (adipokines, free fatty acids (FFA), reactive oxygen species (ROS)) provide clues to the increased incidence and prevalence of OA in obesity. Recently, research found greater OA prevalence and incidence in obese patients with cardiometabolic disturbances than "healthy" obese patients, which led to the description of a new OA phenotype - metabolic syndrome (MetS)-associated OA. Indeed, individual metabolic factors (diabetes, dyslipidemia, and hypertension) may increase the risk of obesity-induced OA. This review discusses hypotheses based on pathways specific to a metabolic factor in MetS-associated OA, such as the role of advanced glycation end products (AGEs) and glucose toxicity. A better understanding of these phenotypes based on risk factors will be critical for designing trials of this specific subset of OA.

Collagen Induced Arthritis in DBA/1J Mice Associates with Oxylipin Changes in Plasma

Oxylipins play important roles in various biological processes and are considered as mediators of inflammation for a wide range of diseases such as rheumatoid arthritis (RA). The purpose of this research was to study differences in oxylipin levels between a widely used collagen induced arthritis (CIA) mice model and healthy control (Ctrl) mice. DBA/1J male mice (age: 6-7 weeks) were selected and randomly divided into two groups, namely, a CIA and a Ctrl group. The CIA mice were injected intraperitoneally (i.p.) with the joint cartilage component collagen type II (CII) and an adjuvant injection of lipopolysaccharide (LPS). Oxylipin metabolites were extracted from plasma for each individual sample using solid phase extraction (SPE) and were detected with high performance liquid chromatography/tandem mass spectrometry (HPLC-ESI-MS/MS), using dynamic multiple reaction monitoring (dMRM). Both univariate and multivariate statistical analyses were applied. The results in univariate Student's t-test revealed 10 significantly up- or downregulated oxylipins in CIA mice, which were supplemented by another 6 additional oxylipins, contributing to group clustering upon multivariate analysis. The dysregulation of these oxylipins revealed the presence of ROS-generated oxylipins and an increase of inflammation in CIA mice. The results also suggested that the collagen induced arthritis might associate with dysregulation of apoptosis, possibly inhibited by activated NF-κB because of insufficient PPAR-γ ligands.

The Role of PPARγ in Advanced Glycation End Products-Induced Inflammatory Response in Human Chondrocytes

Objective

Advances made in the past ten years highlight the notion that peroxisome proliferator-activated receptors gamma (PPARγ) has protective properties in the pathophysiology of osteoarthritis (OA). The aim of this study was to define the roles of PPARγ in AGEs-induced inflammatory response in human chondrocytes.

Methods

Primary human chondrocytes were stimulated with AGEs in the presence or absence of neutralizing antibody against RAGE (anti-RAGE), MAPK specific inhibitors and PPARγ agonist pioglitazone. The expression of IL-1, MMP-13, TNF-α, PPARγ, nuclear NF-κB p65 and cytosol IκBα was determined by western blotting and real-time PCR.

Results

AGEs could enhance the expression of IL-1, TNF-α, and MMP-13, but the level of PPARγ was decreased in a time- and dose-dependent manner, which was inhibited by anti-RAGE, SB203580 (P38 MAPK specific inhibitor) and SP600125 (a selective inhibitor of JNK). PPARγ agonist pioglitazone could inhibit the effects of AGEs-induced inflammatory response and PPARγ down-regulation. In human chondrocytes, AGEs could induce cytosol IκBα degradation and increase the level of nuclear NF-κB p65, which was inhibited by PPARγ agonist pioglitazone.

Conclusions

In primary human chondrocytes, AGEs could down-regulate PPARγ expression and increase the inflammatory mediators, which could be reversed by PPARγ agonist pioglitazone. Activation of RAGE by AGEs triggers a cascade of downstream signaling, including MAPK JNK/ p38, PPARγ and NF-κB. Taken together, PPARγ could be a potential target for pharmacologic intervention in the treatment of OA.

Rheumatoid arthritis and the biological clock

Rheumatoid arthritis (RA) is an autoimmune disease of unknown cause and a chronic and progressive inflammatory disorder ensuing in genetically predisposed subjects, characterized by synovitis causing joint destruction, as well as inflammation in body organ systems, leading to anatomical alteration and functional disability. Immune competent cells, deregulated synoviocytes and cytokines play a key role in the pathophysiological mechanisms. The immune system function shows time-related variations related to the influence of the neuroendocrine system and driven by the circadian clock circuitry. Immune processes and symptom intensity in RA are characterized by oscillations during the day following a pattern of circadian rhythmicity. A cross-talk between inflammatory and circadian pathways is involved in RA pathogenesis and underlies the mutual actions of disruption of the circadian clock circuitry on immune system function as well as of inflammation on the function of the biological clock. Modulation of molecular processes and humoral factors mediating in RA the interplay between the biological clock and the immune response and underlying the rhythmic fluctuations of pathogenic processes and symptomatology could represent a promising therapeutic strategy in the future.

Prostatic protective nature of the flavonoid-rich fraction from Cyclosorus acuminatus on carrageenan-induced non-bacterial prostatitis in rat

Abstract Context: Cyclosorus acuminatus (Houtt.) Nakai (Thelypteridaceae) is used in Chinese traditional medicine for inflammation and pyretic stranguria. Objective: This study investigates the prostatic protective potential of the flavonoid-rich [(2S)-5,7,5'-trihydroxyflavanone glycosides] fraction from C. acuminatus (FCA). Materials and methods: Chronic non-bacterial prostatitis (CNBP) was induced by injecting 20 μl of 1% carrageenan into the rat prostate. Subsequently, FCA (150 or 300 mg/kg/d) was orally given once a day for 4 weeks. Finally, the levels of proinflammatory cytokines and the prostatic expression of peroxisome proliferator activated receptor-γ (PPAR-γ) were evaluated. Results: Treatment with 300 mg/kg/d FCA ameliorated the carrageenan-induced higher prostatic index (PI) state and proinflammatory cytokines levels (NFκB from 2602 ± 588 to 1348 ± 300 pg/ml, TNF-α from 151.6 ± 10.4 to 126.0 ± 3.52 pg/ml, IL-1β from 153.7 ± 14.8 to 63.9 ± 6.7 pg/ml, COX-2 from 313.3 ± 16.5 to 263.1 ± 15.1 pg/ml, PGE from 1532 ± 130 to 864 ± 126 pg/ml, NOS from 33.7 ± 3.0 to 23.6 ± 1.6 U/mg protein, and NO from 40.3 ± 2.9 to 27.1 ± 2.9 μmol/g protein) as well as regulated the prostatic expression of PPAR-γ (increased about 3.50-fold) when compared to the rat model of prostatitis. Discussion and conclusion: FCA could exert a prostatic protective response via modulating the prostatic expression of PPAR-γ and eventually alleviating the NFκB dependent inflammatory response.

The peroxisome proliferator activated receptor-γ pioglitazone improves vascular function and decreases disease activity in patients with rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is associated with heightened mortality due to atherosclerotic cardiovascular disease (CVD). Inflammatory pathways in RA negatively affect vascular physiology and promote metabolic disturbances that contribute to CVD. We hypothesized that the peroxisome proliferator activated receptor‐γ (PPAR‐γ) pioglitazone could promote potent vasculoprotective and anti‐inflammatory effects in RA.

Methods and Results

One hundred forty‐three non‐diabetic adult RA patients (76.2% female, age 55.2±12.1 [mean±SD]) on stable RA standard of care treatment were enrolled in a randomized, double‐blind placebo controlled crossover trial of 45 mg daily pioglitazone versus placebo, with a 3‐month duration/arm and a 2‐month washout period. Pulse wave velocity of the aorta (PWV), brachial artery flow mediated dilatation (FMD), nitroglycerin mediated dilatation (NMD), microvascular endothelial function (reactive hyperemia index [RHI]), and circulating biomarkers of inflammation, insulin resistance, and atherosclerosis risk all were quantified. RA disease activity was assessed with the 28‐Joint Count Disease Activity Score (DAS‐28) C‐reactive protein (CRP) and the Short Form (36) Health Survey quality of life questionnaire. When added to standard of care RA treatment, pioglitazone significantly decreased pulse wave velocity (ie, aortic stiffness) (P=0.01), while FMD and RHI remained unchanged when compared to treatment with placebo. Further, pioglitazone significantly reduced RA disease activity (P=0.02) and CRP levels (P=0.001), while improving lipid profiles. The drug was well tolerated.

Conclusions

Addition of pioglitazone to RA standard of care significantly improves aortic elasticity and decreases inflammation and disease activity with minimal safety issues. The clinical implications of these findings remain to be established.

Clinical Trial Registration

URL: ClinicalTrials.gov Unique Identifier: NCT00554853.

Advanced glycation end products induce peroxisome proliferator-activated receptor γ down-regulation-related inflammatory signals in human chondrocytes via Toll-like receptor-4 and receptor for advanced glycation end products

Accumulation of advanced glycation end products (AGEs) in joints is important in the development of cartilage destruction and damage in age-related osteoarthritis (OA). The aim of this study was to investigate the roles of peroxisome proliferator-activated receptor γ (PPARγ), toll-like receptor 4 (TLR4), and receptor for AGEs (RAGE) in AGEs-induced inflammatory signalings in human OA chondrocytes. Human articular chondrocytes were isolated and cultured. The productions of metalloproteinase-13 and interleukin-6 were quantified using the specific ELISA kits. The expressions of related signaling proteins were determined by Western blotting. Our results showed that AGEs enhanced the productions of interleukin-6 and metalloproteinase-13 and the expressions of cyclooxygenase-2 and high-mobility group protein B1 and resulted in the reduction of collagen II expression in human OA chondrocytes. AGEs could also activate nuclear factor (NF)-κB activation. Stimulation of human OA chondrocytes with AGEs significantly induced the up-regulation of TLR4 and RAGE expressions and the down-regulation of PPARγ expression in a time- and concentration-dependent manner. Neutralizing antibodies of TLR4 and RAGE effectively reversed the AGEs-induced inflammatory signalings and PPARγ down-regulation. PPARγ agonist pioglitazone could also reverse the AGEs-increased inflammatory signalings. Specific inhibitors for p38 mitogen-activated protein kinases, c-Jun N-terminal kinase and NF-κB suppressed AGEs-induced PPARγ down-regulation and reduction of collagen II expression. Taken together, these findings suggest that AGEs induce PPARγ down-regulation-mediated inflammatory signalings and reduction of collagen II expression in human OA chondrocytes via TLR4 and RAGE, which may play a crucial role in the development of osteoarthritis pathogenesis induced by AGEs accumulation.

Peroxisome proliferator-activated receptor γ agonists reduce cell proliferation and viability and increase apoptosis in systemic sclerosis fibroblasts

BACKGROUND

 No study has evaluated the effect of the peroxisome proliferator-activated receptor γ (PPARγ) agonists on cell viability, proliferation and apoptosis in cultured systemic sclerosis (SSc) fibroblasts.

OBJECTIVES

The effects of two pure PPARγ agonists (rosiglitazone and pioglitazone) in cultured SSc fibroblasts were evaluated and compared with effects in normal fibroblasts.

METHODS

 The study included evaluation of cell viability and proliferation (based on the cleavage of tetrazolium salts and measurement of absorbance of the cell proliferation reagent WST-1), and determination of cell apoptosis (by means of the Hoechst dye uptake).

RESULTS

Rosiglitazone or pioglitazone (20μmolL(-1) ) significantly reduced cell proliferation (cell count of 75% and 83% compared with baseline, respectively, after 2h) and cell viability (absorbance reductions of 25% and 22% compared with baseline, respectively, after 2 h), and increased apoptosis (apoptotic cell percentages 9·9% and 8·6%, respectively, after 48h of incubation) in SSc fibroblasts, whereas they did not present a significant influence on control fibroblasts.

CONCLUSIONS

The effects of rosiglitazone or pioglitazone shown on SSc fibroblasts raise the hypothesis of a therapeutic role for PPARγ agonists in patients affected by SSc.

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

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

Effects of diacerein at the molecular level in the osteoarthritis disease process

In osteoarthritis (OA), the alterations in joint tissues are numerous and involve morphological, biochemical and metabolic changes and an upregulation of the inflammatory pathways. The focus of this article is a brief narrative review of the effects of diacerein, an antirheumatic drug from the anthraquinone chemical class, and its active metabolite, rhein, on the factors that participate in the complex interaction between OA tissues and cells leading to the progression of joint structural changes.

Peroxisome proliferator-activated receptor-gamma expression in monocytes/macrophages from rheumatoid arthritis patients: relation to disease activity and therapy efficacy--a pilot study

OBJECTIVES

Peroxisome proliferator-activated receptor-gamma (PPARγ) is expressed by different cell types in the joints and plays a relevant anti-inflammatory role in various diseases. This pilot study aimed to evaluate PPARγ expression in monocytes/macrophages isolated from RA patients as compared with healthy subjects, the relationships between PPARγ expression, MMP-9 activity and disease, and the influence of therapy with anti-rheumatic drugs on these parameters.

METHODS

Thirty RA patients of both sexes (treated with CSs and MTX, mainly) and 15 healthy volunteers were enrolled in this study. Disease severity was evaluated by the 28-joint disease activity score (DAS-28). Monocytes and monocyte-derived macrophages (MDMs) were isolated by standard procedures. PPARγ protein and mRNA expression were assessed by immunoblotting and real-time PCR, respectively; MMP-9 activity was determined by gelatin zymography. Moreover, we checked the ability of 15-deoxy-Δ(12,14)-prostaglandin J(2) (15d-PGJ, a PPARγ agonist), MTX and methylprednisolone (MP) to affect PPARγ expression and lipopolysaccharide (LPS)-induced MMP-9 activity.

RESULTS

Monocytes/MDMs from RA patients have significantly enhanced PPARγ expression (both protein and mRNA) and MMP-9 activity as compared with healthy donors. Interestingly, cells from patients with less active disease (DAS-28 <3.2) present higher PPARγ protein expression and lower MMP-9 activity than RA patients with DAS-28 >3.2. At therapeutic concentrations, MTX and MP increase in vitro PPARγ protein expression and inhibit LPS-induced MMP-9 activity.

CONCLUSION

PPARγ expression in human monocytes/MDMs could represent an indicator of disease activity and therapy efficacy in RA because patients with a DAS-28 score <3.2 show the highest expression.

Egr-1 contributes to IL-1-mediated down-regulation of peroxisome proliferator-activated receptor γ expression in human osteoarthritic chondrocytes

INTRODUCTION

Peroxisome proliferator-activated receptor (PPAR)γ has been shown to exhibit anti-inflammatory and anti-catabolic properties and to be protective in animal models of osteoarthritis (OA). We have previously shown that interleukin-1β (IL-1) down-regulates PPARγ expression in human OA chondrocytes. However, the mechanisms underlying this effect have not been well characterized. The PPARγ promoter harbors an overlapping Egr-1/specificity protein 1 (Sp1) binding site. In this study, our objective was to define the roles of Egr-1 and Sp1 in IL-1-mediated down-regulation of PPARγ expression.

METHODS

Chondrocytes were stimulated with IL-1 and the expression levels of Egr-1 and Sp1 mRNAs and proteins were evaluated using real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting, respectively. The role of de novo protein synthesis was evaluated using the protein synthesis inhibitor cycloheximide (CHX). The recruitment of Sp1 and Egr-1 to the PPARγ promoter was evaluated using chromatin immunoprecipitation (ChIP) assays. The PPARγ promoter activity was analyzed in transient transfection experiments. The roles of Egr-1 and Sp1 were further evaluated using small interfering RNA (siRNA) approaches. The level of Egr-1 in cartilage was determined using immunohistochemistry.

RESULTS

Down-regulation of PPARγ expression by IL-1 requires de novo protein synthesis and was concomitant with the induction of the transcription factor Egr-1. Treatment with IL-1 induced Egr-1 recruitment and reduced Sp1 occupancy at the PPARγ promoter. Overexpression of Egr-1 potentiated, whereas overexpression of Sp1 alleviated, the suppressive effect of IL-1 on the PPARγ promoter, suggesting that Egr-1 may mediate the suppressive effect of IL-1. Consistently, Egr-1 silencing prevented IL-1-mediated down-regulation of PPARγ expression. We also showed that the level of Egr-1 expression was elevated in OA cartilage compared to normal cartilage.

CONCLUSIONS

Our results indicate that induction and recruitment of Egr-1 contributed to the suppressive effect of IL-1 on PPARγ expression. They also suggest that modulation of Egr-1 levels in the joint may have therapeutic potential in OA.

Microarray Analysis of the Infrapatellar Fat Pad in Knee Osteoarthritis: Relationship with Joint Inflammation

Objective.

To examine differences in genes involved in fat metabolism, energy homeostasis, adipogenesis, and inflammation between endstage and early-stage knee osteoarthritis (OA) infrapatellar fat pads (IFP).

Methods.

Twenty-nine endstage and 5 early-stage primary OA IFP were harvested at knee surgery. Total RNA was extracted, labeled, and hybridized to whole-genome expression arrays. Unsupervised analysis of all samples using principal components analysis or 2-way hierarchical clustering showed groupings based on tissue source and disease. Statistical testing identified sets of genes that displayed differences between the 2 fat types. Western blot analysis was performed for protein expression of an identified gene of interest.

Results.

The 29 IFP demonstrated an elevation in the expression of adipokines such as adiponectin and leptin. A statistically significant increased expression was seen for genes of adipogenesis, such as peroxisome proliferator-activated receptor-γ (PPAR-γ), diacylglycerol acyltransferase 2 (DGAT2), cluster of differentiation (CD36), and thyroid hormone responsive spot (THRSP) in the severe OA fat pads as compared to the controls. A subset of 5 patients in the endstage OA group were consistently similar in gene expression to early OA tissue. Protein expression of PPAR-γ2 was 5.4-fold and PPAR-γ1 was 1.4-fold greater in endstage versus early OA tissue.

Conclusion.

Endstage OA fat pads demonstrated a significant upregulation of genes for fat metabolism and energy homeostasis and a mixed result for inflammatory cytokines.

Peroxisome proliferator-activated receptor gamma in osteoarthritis

Osteoarthritis (OA) is among the most prevalent chronic human health disorders and the most common form of arthritis. It is a leading cause of disability in developed countries. This disease is characterized by cartilage deterioration, synovitis, and remodeling of the subchondral bone. There is not yet a satisfactory treatment to stop or arrest this disease process. Although several candidates for therapeutic approaches have been put forward, recent studies suggest that activation of the transcription factor peroxisome proliferator-activated receptor gamma (PPARγ) is an interesting target for this disease. PPARγ is a ligand-activated transcription factor and member of the nuclear receptor superfamily. Agonists of PPARγ inhibit inflammation and reduce synthesis of cartilage degradation products both in vitro and in vivo, and reduce the development/progression of cartilage lesions in OA animal models. This review will highlight the recent experimental studies on the presence of PPARγ in articular tissues and its effect on inflammatory and catabolic responses in chondrocytes and synovial fibroblasts, as well as the protective effects of PPARγ ligands in arthritis experimental models. Finally, the role of PPARγ polymorphism in the pathogenesis of OA and related musculoskeletal diseases will also be discussed.

[Pathophysiological relevance of peroxisome proliferators activated receptors (PPAR) to joint diseases - the pro and con of agonists]

Peroxisome proliferators activated receptors (PPAR) are ligand-inducible nuclear transacting factors comprising three subtypes, PPARalpha, PPARbeta/delta and PPARgamma, which play a key role in lipids and glucose homeostasis. All PPAR subtypes have been identified in joint or inflammatory cells and their activation resulted in a transcriptional repression of pro-inflammatory cytokines (IL-1, TNFalpha), early inflammatory genes (NOS(2), COX-2, mPGES-1) or matrix metalloproteases (MMP-1, MMP-13), at least for the gamma subtype. PPAR full agonists were also shown to stimulate IL-1 receptor antagonist (IL-1Ra) production by cytokine-stimulated articular cells in a subtype-dependent manner. These anti-inflammatory and anti-catabolic properties were confirmed in animal models of joint diseases where PPAR agonists reduced synovial inflammation while preventing cartilage destruction or inflammatory bone loss, although many effects required much higher doses than needed to restore insulin sensitivity or to lower circulating lipid levels. However, these promising effects of PPAR full agonists were hampered by their ability to reduce the growth factor-dependent synthesis of extracellular matrix components or to induce chondrocyte apoptosis, by the possible contribution of immunosuppressive properties to their anti-arthritic effects, by the increased adipocyte differentiation secondary to prolonged stimulation of PPARgamma, and by a variable contribution of PPAR subtypes depending on the system. Clinical data are scarce in rheumatoid arthritis (RA) patients whereas thousands of patients worldwilde, treated with PPAR agonists for type 2 diabetes or dyslipidemia, are paradoxically prone to suffer from osteoarthritis (OA). Whereas high dosage of full agonists may expose RA patients to cardiovascular adverse effects, the proof of concept that PPAR agonists have therapeutical relevance to OA may benefit from an epidemiological follow-up of joint lesions in diabetic or hyperlipidemic patients treated for long periods of time with glitazones or fibrates. Additionally, cellular and animal studies are required to assess whether partial agonists of PPAR (SPPARMs) may preserve therapeutical properties with potentially less safety concern.

Anti-adult T-cell leukemia effects of a novel synthetic retinoid, Am80 (Tamibarotene)

Clinical trials for treatment of adult T-cell leukemia (ATL) caused by human T-cell leukemia virus type I (HTLV-I) using all-trans-retinoic acid (ATRA) have shown satisfactory therapeutic responses, although efficacies were limited. Recently, many synthetic retinoids have been developed and among them, a novel synthetic retinoid, Am80 (Tamibarotene) is an RARalpha- and RARbeta-specific retinoid expected to overcome ATRA resistance. The present study examined the inhibitory effects of Am80 on HTLV-I-infected T-cell lines and ATL cells. Am80 had negligible growth inhibition of peripheral blood mononuclear cells but marked growth inhibition of both HTLV-I-infected T-cell lines and ATL cells. Am80 arrested cells in the G1 phase of the cell cycle and induced apoptosis in HTLV-I-infected T-cell lines. It inhibited also the phosphorylation of IkappaBalpha and NF-kappaB-DNA binding, in conjunction with reduction of expression of proteins involved in the G1/S cell cycle transition and apoptosis. Am80 also inhibited the expression of JunD, resulting in suppression of AP-1-DNA binding. Furthermore, severe combined immunodeficient mice with tumors induced by subcutaneous inoculation of HTLV-I-infected T cells, responded to Am80 treatment with partial regression of tumors and no side-effects. These findings demonstrate that Am80 is a potential inhibitor of NF-kappaB and AP-1, and is a potentially useful therapeutic agent against ATL.

A 9-cis beta-carotene-enriched diet inhibits atherogenesis and fatty liver formation in LDL receptor knockout mice

Our aim was to study the effect of 9-cis beta-carotene-rich powder of the alga Dunaliella bardawil on lipid profile, atherogenesis, and liver steatosis in high-fat diet-fed LDL receptor knockout mice. In 4 sets of experiments, mice were distributed into the following groups: control, fed an unfortified diet; Dunaliella 50, fed a diet composed of 50% 9-cis and 50% all-trans beta-carotene; Dunaliella 25, fed a diet containing 25% 9-cis and 75% all-trans beta-carotene; beta-carotene-deficient Dunaliella, fed beta-carotene-deficient Dunaliella powder; and all-trans beta-carotene, fed a synthetic all-trans beta-carotene. All fortified diets contained 0.6% total beta-carotene. Algal 9-cis beta-carotene was absorbed by the mice and accumulated in the liver. Synthetic all-trans beta-carotene was not converted to 9-cis beta-carotene. Dunaliella 50 inhibited high-fat diet-induced plasma cholesterol elevation by 40-63% and reduced cholesterol concentrations in the atherogenic VLDL and LDL. Atherosclerotic lesion area in mice treated with Dunaliella 50 was 60-83% lower compared with mice fed the high-fat diet alone. beta-Carotene-deficient Dunaliella did not influence plasma cholesterol and atherogenesis, suggesting that beta-carotene is essential for a Dunaliella protective effect. Moreover, by administrating Dunaliella powder containing different levels of 9-cis and all-trans beta-carotene isomers, we found that the effect on plasma cholesterol concentration and atherogenesis is 9-cis-dependent. Dunaliella 50 also inhibited fat accumulation and inflammation in the livers of mice fed a high-fat diet, which was accompanied by reduced mRNA levels of inflammatory genes. These results in mice suggest that 9-cis beta-carotene may have the potential to inhibit atherogenesis in humans.

Peroxisome proliferator-activated receptor gamma1 expression is diminished in human osteoarthritic cartilage and is downregulated by interleukin-1beta in articular chondrocytes

Peroxisome proliferator-activated receptor γ (PPARγ) is a nuclear receptor involved in the regulation of many cellular processes. We and others have previously shown that PPARγ activators display anti-inflammatory and chondroprotective properties in vitro and improve the clinical course and histopathological features in an experimental animal model of osteoarthritis (OA). However, the expression and regulation of PPARγ expression in cartilage are poorly defined. This study was undertaken to investigate the quantitative expression and distribution of PPARγ in normal and OA cartilage and to evaluate the effect of IL-1β, a prominent cytokine in OA, on PPARγ expression in cultured chondrocytes. Immunohistochemical analysis revealed that the levels of PPARγ protein expression were significantly lower in OA cartilage than in normal cartilage. Using real-time RT-PCR, we demonstrated that PPARγ1 mRNA levels were about 10-fold higher than PPARγ2 mRNA levels, and that only PPARγ1 was differentially expressed: its levels in OA cartilage was 2.4-fold lower than in normal cartilage (p < 0.001). IL-1 treatment of OA chondrocytes downregulated PPARγ1 expression in a dose- and time-dependent manner. This effect probably occurred at the transcriptional level, because IL-1 decreases both PPARγ1 mRNA expression and PPARγ1 promoter activity. TNF-α, IL-17, and prostaglandin E₂ (PGE₂), which are involved in the pathogenesis of OA, also downregulated PPARγ1 expression. Specific inhibitors of the mitogen-activated protein kinases (MAPKs) p38 (SB203580) and c-Jun N-terminal kinase (SP600125), but not of extracellular signal-regulated kinase (PD98059), prevented IL-1-induced downregulation of PPARγ1 expression. Similarly, inhibitors of NF-κB signaling (pyrrolidine dithiocarbamate, MG-132, and SN-50) abolished the suppressive effect of IL-1. Thus, our study demonstrated that PPARγ1 is downregulated in OA cartilage. The pro-inflammatory cytokine IL-1 may be responsible for this downregulation via a mechanism involving activation of the MAPKs (p38 and JNK) and NF-κB signaling pathways. The IL-1-induced downregulation of PPARγ expression might be a new and additional important process by which IL-1 promotes articular inflammation and cartilage degradation.

The peroxisome proliferator-activated receptor gamma agonist pioglitazone reduces the development of cartilage lesions in an experimental dog model of osteoarthritis: in vivo protective effects mediated through the inhibition of key signaling and catabolic pathways

OBJECTIVE

Emerging evidence indicates that peroxisome proliferator-activated receptor gamma (PPARgamma) may have protective effects in osteoarthritis (OA). The aim of this study was to evaluate the in vivo effect of a PPARgamma agonist, pioglitazone, on the development of lesions in a canine model of OA, and to explore the influence of pioglitazone on the major signaling and metabolic pathways involved in OA pathophysiologic changes.

METHODS

OA was surgically induced in dogs by sectioning of the anterior cruciate ligament. The dogs were then randomly divided into 3 treatment groups in which they were administered either placebo, 15 mg/day pioglitazone, or 30 mg/day pioglitazone orally for 8 weeks. Following treatment, the severity of cartilage lesions was scored. Cartilage specimens were processed for histologic and immunohistochemical evaluations; specific antibodies were used to study the levels of matrix metalloproteinase 1 (MMP-1), ADAMTS-5, and inducible nitric oxide synthase (iNOS), as well as phosphorylated MAPKs ERK-1/2, p38, JNK, and NF-kappaB p65.

RESULTS

Pioglitazone reduced the development of cartilage lesions in a dose-dependent manner, with the highest dosage producing a statistically significant change (P < 0.05). This decrease in lesions correlated with lower cartilage histologic scores. In addition, pioglitazone significantly reduced the synthesis of the key OA mediators MMP-1, ADAMTS-5, and iNOS and, at the same time, inhibited the activation of the signaling pathways for MAPKs ERK-1/2, p38, and NF-kappaB.

CONCLUSION

These results indicate the efficacy of pioglitazone in reducing cartilage lesions in vivo. The results also provide new and interesting insights into a therapeutic intervention for OA in which PPARgamma activation can inhibit major signaling pathways of inflammation and reduce the synthesis of cartilage catabolic factors responsible for articular cartilage degradation.

Sequential induction of pro- and anti-inflammatory prostaglandins and peroxisome proliferators-activated receptor-gamma during normal wound healing: a time course study

Lipid mediators generated from metabolism of arachidonic acid play a crucial role in the initiating and resolution of acute inflammation by shifting from pro-inflammatory prostaglandin (PG) E2 to anti-inflammatory PGD2 and its metabolites. The changes in PG levels over time during the normal wound-repair process have not, however, been reported. We determined the temporal expression of PG and their biosynthetic enzymes using the full thickness incisional model of normal wound healing in mice. We demonstrate that during normal wound repair, there is a shift in the metabolism of arachidonate from PGE2 during the acute inflammatory phase to PGD2 during the repair phase. This shift is mediated by temporal changes in the expression of cyclooxygenases (COX) and microsomal PGES (mPGES)-1. Inducible COX (COX-2) expression is sustained throughout the initiation and repair process, but mPGES-1 is increased only during the acute inflammatory phase and its disappearance coincides with increased PGD2. PGD2 and its degradation products are known to mediate their anti-inflammatory effects by binding to peroxisome proliferators-activated receptor gamma (PPARgamma). In this study, we show that PPARgamma is upregulated during the resolution phase of wound repair concomitant with the shift to PGD2, and may be responsible for initiating endogenous mechanism resulting in healing/resolution.

Peroxisome-proliferator-activated receptor-gamma (PPARgamma) activation protects neurons from NMDA excitotoxicity

A growing body of evidence indicates that the transcription factor PPARgamma plays a beneficial role in various neurological diseases. The postulated principal mechanism underlying the beneficial effects of PPARgamma is due to its anti-inflammatory properties. However, PPARgamma exists in neurons where it may provide additional effects that regulate neuronal vulnerability. In the present study, we employed in vitro and in vivo models of excitotoxic neuronal injury to test hypothesis on the neuroprotective role of PPARgamma. The endogenous PPARgamma ligand, 15d-Delta(12,14)-Prostaglandin J2 (15d-PGJ2), and a selective thiazolidinedione PPARgamma agonist, ciglitazone, significantly reduced neuronal death in response to glutamate and NMDA-mediated, but not kainate-mediated toxicity. This neuroprotective effect of 15d-PGJ2 and ciglitazone was linked to increased PPARgamma DNA binding activity as it was fully reversed by the pretreatment of neurons with selective PPARgamma antagonists and anti-PPARgamma antibody. It was not due to the blockade of NMDA-receptor-mediated Ca++ entry. Our data demonstrate that PPARgamma activation may represent a potential target for treatment of numerous acute and chronic neurological diseases with pathologies that involve excitotoxic damage.

Peroxisome proliferator-activated receptors and inflammation

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptors family. PPARs are a family of 3 ligand-activated transcription factors: PPARalpha (NR1C1), PPARbeta/delta (NUC1; NR1C2), and PPARgamma (NR1C3). PPARalpha, -beta/delta, and -gamma are encoded by different genes but show substantial amino acid similarity, especially within the DNA and ligand binding domains. All PPARs act as heterodimers with the 9-cis-retinoic acid receptors (retinoid X receptor; RXRs) and play important roles in the regulation of metabolic pathways, including those of lipid of biosynthesis and glucose metabolism, as well as in a variety of cell differentiation, proliferation, and apoptosis pathways. Recently, there has been a great deal of interest in the involvement of PPARs in inflammatory processes. PPAR ligands, in particular those of PPARalpha and PPARgamma, inhibit the activation of inflammatory gene expression and can negatively interfere with pro-inflammatory transcription factor signaling pathways in vascular and inflammatory cells. Furthermore, PPAR levels are differentially regulated in a variety of inflammatory disorders in man, where ligands appear to be promising new therapies.

Antihyperalgesic properties of the cannabinoid CT-3 in chronic neuropathic and inflammatory pain states in the rat

CT-3 (ajulemic acid) is a synthetic analogue of a metabolite of Delta9-tetrahydrocannabinol that has reported analgesic efficacy in neuropathic pain states in man. Here we show that CT-3 binds to human cannabinoid receptors in vitro, with high affinity at hCB1 (Ki 6 nM) and hCB2 (Ki 56 nM) receptors. In a functional GTP-gamma-S assay CT-3 was an agonist at both hCB1 and hCB2 receptors (EC50 11 and 13.4 nM, respectively). In behavioural models of chronic neuropathic and inflammatory pain in the rat, oral administration of CT-3 (0.1-1 mg/kg) produced up to 60% reversal of mechanical hyperalgesia. In both models the antihyperalgesic activity was prevented by the CB1-antagonist SR141716A but not the CB2-antagonist SR144528. In the tetrad of tests for CNS activity, CT-3 (1-10 mg/kg, po) produced dose-related catalepsy, deficits in locomotor performance, hypothermia, and acute analgesia. Comparison of 50% maximal effects in the tetrad and chronic pain assays produced an approximate therapeutic index of 5-10. Pharmacokinetic analysis showed that CT-3 exhibits significant but limited brain penetration, with a brain/plasma ratio of 0.4 measured following oral administration, compared to ratios of 1.0-1.9 measured following subcutaneous administration of WIN55,212-2 or Delta9-THC. These data show that CT-3 is a cannabinoid receptor agonist and is efficacious in animal models of chronic pain by activation of the CB1 receptor. Whilst it shows significant cannabinoid-like CNS activity, it exhibits a superior therapeutic index compared to other cannabinoid compounds, which may reflect a relatively reduced CNS penetration.

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

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