PPARgamma Activation Research Articles

Metabolic syndrome-interdependence of the cardiovascular and metabolic pathways

The metabolic syndrome is a worldwide epidemic, setting the stage for type 2 diabetes and its microvascular complications, and acceleration of macrovascular disease. Insulin resistance, hyperglycemia, dyslipidemia, hypertension, thrombotic disorders and adiposity define the metabolic syndrome and contribute to endothelial dysfunction and, subsequently, to accelerated atherosclerosis. Angiotensin II contributes to the development and progression of cardiovascular and renal endpoints and, as such, angiotensin II receptor blockers and angiotensin-converting enzyme inhibitors demonstrate a protective effect. Ligands for the peroxisome proliferator-activated receptor gamma (PPAR gamma), appear to impact favourably on atherosclerosis through both direct and indirect mechanisms. In humans, these ligands improve endothelial function, attenuate albuminuria and hypertension, and potentially prevent conversion of prediabetes to type 2 diabetes. Statins also have proven benefit in decreasing overall cardiovascular and stroke mortality and morbidity. The combination of angiotensin II blockade, statin therapy and PPAR gamma activation might emerge as an important global therapeutic strategy in the metabolic syndrome and diabetes. Further studies are needed to determine whether they have synergistic effects to protect the vasculature.

PPARγ in the control of brown adipocyte differentiation

The effects of fatty acids and retinoic acid (carotene) on brown adipose tissue differentiation are mediated by activation of the transcription factors PPARgamma and PPARalpha in combination with RXR. There is good support for the idea that activated PPARgamma promotes adipogenesis also in brown adipose tissue. However, the issue is more complex concerning the full differentiation to the brown adipocyte phenotype, particularly the expression of the brown-fat-specific marker UCP1. The effect of norepinephrine on PPARgamma gene expression, at least in-vitro, is negative, PPARgamma-ablated brown adipose tissue can express UCP1, and PGC-1alpha coactivates other transcription factors (including PPARalpha); thus, the significance of PPARgamma for the physiological control of UCP1 gene expression is not settled. However, importantly, the effects of PPAR agonists demonstrate the existence of a pathway for brown adipose tissue recruitment that is not dependent on chronic adrenergic stimulation and may be active in recruitment conditions such as prenatal and prehibernation recruitment. The ability of chronic PPARgamma agonist treatment to promote the occurrence of brown-fat features in white adipose tissue-like depots implies a role in anti-obesity treatment, but this will only be effective if the extra thermogenic capacity is activated by adrenergic stimulation.

Atypical transcriptional regulators and cofactors of PPARγ

Regulation of peroxisome proliferator-activated receptor gamma (PPARgamma) activity is the result of several events. The first control level is the regulation of the expression of PPARgamma. Examples of this regulation, during adipogenesis, is the transactivation of the PPARgamma promoter by transcription factors of the classical pathway, such as C/EBPs or ADD1/SREBP1, but also newly identified factors, such as E2Fs. When preadipocytes re-enter the cell cycle, PPARgamma expression is induced coincident with an increase in DNA synthesis, suggesting the involvement of the E2F family of cell cycle regulators. E2F1 induces PPARgamma transcription during clonal expansion, whereas E2F4 represses PPARgamma expression during terminal adipocyte differentiation. Hence, E2Fs represent the link between proliferative signaling pathways, triggering clonal expansion, and terminal adipocyte differentiation through regulation of PPARgamma expression. A second regulatory level of PPARgamma action is interaction with cofactors. We will focus our attention on the atypical PPARgamma modulators. We have described an interaction between PPARgamma and the retinoblastoma protein, RB, which is both dependent upon ligand binding by PPARgamma and upon the phosphorylation status of RB. The interaction between PPARgamma and RB decreases the transcriptional activity of PPARgamma through recruitment of the histone deacetylase HDAC3. Inhibition of HDAC activity consequently results in a strong activation of PPARgamma.

Regulation of PPARγ activity during adipogenesis

Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor regulating an array of diverse functions in a variety of cell types including regulation of genes associated with growth and differentiation. Its most notable function is to regulate development of adipose tissue, which involves coordinating expression of many hundreds of genes responsible for establishment of the mature adipocyte phenotype. Our recent studies have demonstrated a role for MEK/ERK signaling and CCAAT/enhancer binding proteins (C/EBP)beta in regulating expression of PPARgamma during adipogenesis. Furthermore, we have shown that cAMP-dependent signaling along with C/EBPbeta leads to the stimulation of PPARgamma activity by mechanisms that probably involve production of PPARgamma ligands. Additionally, we have recently demonstrated that phosphorylation of C/EBPbeta at a consensus ERK/GSK3 site is required for the PPARgamma-associated expression of adiponectin during the terminal stages of adipogenesis. GSK3beta also influences PPARgamma activity by regulating the turnover and subcellular localization of beta-catenin, a potent transcriptional activator of Wnt signaling. In fact, we have recently shown a crosstalk between PPARgamma and beta-catenin signaling. Specifically, activation of PPARgamma induces the degradation of beta-catenin during preadipocyte differentiation by mechanisms that require GSK3beta and the proteasome. In contrast, expression of a GSK3beta-phosphorylation-defective beta-catenin renders beta-catenin resistant to the degradatory action of PPARgamma. Interestingly, expression of the mutant beta-catenin blocks expression of adiponectin and C/EBPalpha in response to the activation of PPARgamma.

Nuclear receptor peroxisome proliferator‐activated receptor‐γ is activated in rat microglial cells by the anti‐inflammatory drug HCT1026, a derivative of flurbiprofen

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is constitutively expressed in primary cultures of rat microglia, the main population of brain resident macrophages, and its ligand-dependent activation leads to the repression of several microglial functions. A few non-steroidal anti-inflammatory drugs (NSAIDs), e.g. indomethacin and ibuprofen, show PPAR-gamma agonistic properties. It has been proposed that PPAR-gamma activation contributes to the potential benefits of the long-term use of certain NSAIDs in delaying the progression of Alzheimer's disease (AD). Previous data have shown that the NSAID HCT1026 [2-fluoro-alpha-methyl(1,1'-biphenyl)4-acetic acid-4-(nitrooxy)butyl ester], a derivative of flurbiprofen which releases nitric oxide (NO), reduces the number of reactive microglial cells in a variety of models. This evidence together with the chemical analogy with ibuprofen led us to investigate whether flurbiprofen and HCT1026 interact with PPAR-gamma and interfere with microglial activation. We found that a low concentration (1 microm) of HCT1026, but not flurbiprofen, activated PPAR-gamma in primary cultures of rat microglia, with kinetics similar to those of the synthetic agonist ciglitazone. The PPAR-gamma antagonist GW9662 (2-chloro-5-nitrobenzanilide) prevented the activation of PPAR-gamma by HCT1026. Interestingly, unlike other NSAIDs that activate PPAR-gamma at concentrations higher than those required for cyclooxygenase inhibition, HCT1026 activated PPAR-gamma and inhibited prostaglandin E2 synthesis at the same low concentration (1 microm). The results suggest that HCT1026 may exert additional anti-inflammatory actions through PPAR-gamma activation, allowing a more effective control of microglial activation and brain inflammation.

Conjugated Linoleic Acid Attenuates the Production and Gene Expression of Proinflammatory Cytokines in Weaned Pigs Challenged with Lipopolysaccharide

We investigated the anti-inflammatory role of conjugated linoleic acid (CLA) in inflammation-challenged weaned pigs and in in vitro cultured peripheral blood mononuclear cells (PBMCs). To test the hypothesis that inflammation responses can be attenuated by dietary CLA supplementation, we used an acute inflammation model in which pigs were injected with lipopolysaccharide (LPS). After 14 d of dietary supplementation with either 2% soybean oil or 2% CLA, half of the pigs in each diet group were challenged with LPS. Dietary CLA alleviated growth depression and prevented the elevations in production and mRNA expression of proinflammatory cytokines [i.e., interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha] induced by the LPS challenge. CLA enhanced the expression of interleukin-10 (IL-10) and peroxisome proliferator-activated receptor-gamma (PPARgamma) in spleen and thymus. To further elucidate the inhibitory effects and the mechanism of action of CLA on cytokine profiles (i.e., IL-1beta, IL-6, and TNF-alpha), PBMCs were isolated from weaned pigs and cultured in media containing cis-9, trans-11 (9c,11t) CLA and trans-10, cis-12 (10t,12c) CLA. Each CLA isomer suppressed the production and expression of IL-1beta, IL-6, and TNF-alpha, and enhanced PPARgamma activation and gene expression in cultured PBMCs. At the molecular level, the inhibitory actions of CLA on IL-1beta, IL-6, and TNF-alpha are attributable mainly to 10t,12c-CLA and the anti-inflammatory properties of CLA are mediated, at least in part, through a PPARgamma-dependent mechanism.

Linkage to peroxisome proliferator-activated receptor-γ in SAMP1/YitFc mice and in human Crohn’s disease

Genetic predisposition is implicated strongly in Crohn's disease. Disease-associated mutations in NOD2/CARD15 , the best-studied susceptibility gene in this disorder, explain only a small fraction of the heritability. The SAMP1/YitFc (SAMP1/Fc) mouse strain expresses many features of Crohn's disease in humans. We bred SAMP1/Fc to disease-resistant AKR mice to identify additional susceptibility genes that may play a role in human disease. Linkage disequilibrium mapping was performed in an (AKR x SAMP1/Fc) backcross to SAMP1/Fc, followed by sequencing, expression analysis using reverse transcription polymerase chain reaction (PCR) and immunohistochemistry, and functional testing in vivo of the regional candidate gene encoding the peroxisome proliferator-activated receptor gamma ( Pparg ). A cohort-based association study was performed in humans. We show that ileitis is blocked in SAMP1/Fc mice by inheritance of AKR alleles on chromosome 6 in the region of Pparg . Major differences in Ppargamma expression in the parental mouse strains are found specifically in the crypts of the small intestine, and treatment of ileitis-prone mice with a Ppargamma agonist decreased disease severity in susceptible mice expressing low levels of the protein. Rare alleles of PPARG are associated significantly with Crohn's disease in humans. We have identified Pparg as a susceptibility gene in both the SAMP/Yit mouse and in human Crohn's disease. Similarities between Crohn's disease and the SAMP1/Fc model suggest that the effect of this gene in humans may be mediated through regulation of PPARgamma activity in the crypts of the small intestine.

Curcuminoids and Sesquiterpenoids in Turmeric (Curcuma longa L.) Suppress an Increase in Blood Glucose Level in Type 2 Diabetic KK-Ay Mice

Turmeric, the rhizome of Curcuma longa L., has a wide range of effects on human health. The chemistry includes curcuminoids and sesquiterpenoids as components, which are known to have antioxidative, anticarcinogenic, and antiinflammatory activities. In this study, we investigated the effects of three turmeric extracts on blood glucose levels in type 2 diabetic KK-A(y) mice (6 weeks old, n = 5/group). These turmeric extracts were obtained by ethanol extraction (E-ext) to yield both curcuminoids and sesquiterpenoids, hexane extraction (H-ext) to yield sesquiterpenoids, and ethanol extraction from hexane-extraction residue (HE-ext) to yield curcuminoids. The control group was fed a basal diet, while the other groups were fed a diet containing 0.1 or 0.5 g of H-ext or HE-ext/100 g of diet or 0.2 or 1.0 g of E-ext/100 g of diet for 4 weeks. Although blood glucose levels in the control group significantly increased (P < 0.01) after 4 weeks, feeding of 0.2 or 1.0 g of E-ext, 0.5 g of H-ext, and 0.5 g of HE-ext/100 g of diet suppressed the significant increase in blood glucose levels. Furthermore, E-ext stimulated human adipocyte differentiation, and these turmeric extracts had human peroxisome proliferator-activated receptor-gamma (PPAR-gamma) ligand-binding activity in a GAL4-PPAR-gamma chimera assay. Also, curcumin, demethoxycurcumin, bisdemethoxycurcumin, and ar-turmerone had PPAR-gamma ligand-binding activity. These results indicate that both curcuminoids and sesquiterpenoids in turmeric exhibit hypoglycemic effects via PPAR-gamma activation as one of the mechanisms, and suggest that E-ext including curcuminoids and sesquiterpenoids has the additive or synergistic effects of both components.

Peroxisome Proliferator-Activated Receptor γ-Independent Ablation of Cyclin D1 by Thiazolidinediones and Their Derivatives in Breast Cancer Cells

In light of the clinical relevance of targeting cyclin D1 in breast cancer, we have investigated the mechanism underlying the effect of the peroxisome proliferator-activated receptor-gamma (PPARgamma) agonists troglitazone and ciglitazone on cyclin D1 repression. We obtain evidence that the ability of high doses of troglitazone and ciglitazone to repress cyclin D1 is independent of PPARgamma activation. PPARgamma-inactive troglitazone and ciglitazone analogs 5-[4-(6-hydroxy-2,5,7,8-tetramethyl-chroman-2-yl-methoxy)-benzylidene]-2,4-thiazolidinedione (Delta2-TG) and 5-[4-(1-methyl-cyclohexylmethoxy)-benzylidene]-thiazolidine-2,4-dione are able to facilitate cyclin D1 ablation with potency similar to that of troglitazone and ciglitazone in MCF-7 cells. Reverse transcription-polymerase chain reaction shows that the mRNA level of cyclin D1 remains unaltered in drug-treated cells, indicating the repression is mediated at the post-transcriptional level. Moreover, the ablative effect of these agents is specific to cyclin D1, in that the expression levels of many other cyclins and cyclin-dependent kinases examined remain unchanged after drug treatment. Our data indicate that troglitazone- and Delta2-TG-induced cyclin D1 repression is mediated via proteasome-facilitated proteolysis because it is inhibited by different proteasome inhibitors, including N-carbobenzoxy-l-leucinyl-l-leucinyl-l-norleucinal (MG132), lactacystin, and epoxomicin, and is preceded by increased ubiquitination. The dissociation of these two pharmacological activities (i.e., PPARgamma activation and cyclin D1 ablation) provides a molecular basis to use Delta2-TG as a scaffold to develop a novel class of cyclin D1-ablative agents. Therefore, a series of Delta2-TG derivatives have been synthesized. Among them, 5-[4-(6-allyoxy-2,5,7,8-tetramethyl-chroman-2-yl-methoxy)-benzylidene]-2,4-thiazolidinedione represents a structurally optimized agent with potency that is an order of magnitude higher than that of Delta2-TG in cyclin D1 repression and MCF-7 cell growth inhibition.

The role of the orphan nuclear receptor Rev-Erbα in adipocyte differentiation and function

Lipid and carbohydrate homeostasis in higher organisms is governed by an integrated system that has a capacity to rapidly respond to metabolic changes. Numerous signals reciprocally convey information about body fat status from the periphery to central nervous system in the attempt to maintain body weight nearly stable throughout life. The role of adipocyte in energy homeostasis extends its function as a simple energy storage cell. Indeed, adipose tissue not only secretes fatty acids, but is also an active endocrine and paracrine organ due to the production of secreted proteins and lipid indicators collectively called adipokines. These observations have spurred interest in the identification of the transcriptional and other regulatory pathways of adipocyte differentiation. The nuclear receptor, peroxisome proliferator-activated receptor gamma (PPAR gamma) (NR1C3) and members of the CCAAT enhancer-binding protein (C/EBP) family are central mediators controlling adipocyte differentiation and function. Rev-erb alpha (NR1D1) is an orphan nuclear receptor encoded on the opposite strand of the thyroid receptor alpha gene. Rev-erb alpha acts as a negative regulator of transcription binding to the same response element than another orphan nuclear receptor, ROR alpha. Rev-erb alpha is highly expressed in adipose tissue, skeletal muscle, heart, liver and brain. Rev-erb alpha expression increases during adipocyte differentiation of 3T3-L1 cells and is induced by PPAR gamma activation in both 3T3-L1 cells in vitro and in rat adipose tissue in vivo via a direct repeat (DR2) in the Rev-erb alpha promoter. Ectopic expression of Rev-erb alpha potentiates the adipocyte differentiation in 3T3-L1 cells. Recent results in vascular smooth muscle cells (VSMCs) indicate that Rev-erb alpha also controls inflammation by regulating NF-kappa B responsive genes, such as IL-6 and COX-2. Future studies on a potential role of Rev-erb alpha on glucose homeostasis and/or inflammation control are thus warranted.

Antidiabetic thiazolidinediones induce ductal differentiation but not apoptosis in pancreatic cancer cells

Thiazolidinediones (TZD) are a new class of oral antidiabetic drugs that have been shown to inhibit growth of same epithelial cancer cells. Although TZD were found to be ligands for peroxisome proliferator-activated receptor gamma (PPARgamma), the mechanism by which TZD exert their anticancer effect is presently unclear. In this study, we analyzed the mechanism by which TZD inhibit growth of human pancreatic carcinoma cell lines in order to evaluate the potential therapeutic use of these drugs in pancreatic adenocarcinoma. The effects of TZD in pancreatic cancer cells were assessed in anchorage-independent growth assay. Expression of PPARgamma was measured by reverse-transcription polymerase chain reaction and confirmed by Western blot analysis. PPARgamma activity was evaluated by transient reporter gene assay. Flow cytometry and DNA fragmentation assay were used to determine the effect of TZD on cell cycle progression and apoptosis respectively. The effect of TZD on ductal differentiation markers was performed by Western blot. Exposure to TZD inhibited colony formation in a PPARgamma-dependent manner. Growth inhibition was linked to G1 phase cell cycle arrest through induction of the ductal differentiation program without any increase of the apoptotic rate. TZD treatment in pancreatic cancer cells has potent inhibitory effects on growth by a PPAR-dependent induction of pancreatic ductal differentiation.

Peroxisome Proliferator-Activated Receptors and their Ligands

Glucocorticoids have remained one of the most frequently used classes of drugs for the treatment of skin diseases since their introduction more than 50 years ago. As a result of the discovery of new members of the nuclear hormone receptor (NR) superfamily, alternative therapeutic interventions that target retinoid and vitamin D receptors have been developed. Peroxisome proliferator-activated receptors (PPARs) comprise another important NR subfamily, consisting of three different isotypes: PPARalpha, PPARdelta (PPARbeta) and PPARgamma. These NRs are activated by a variety of natural and synthetic ligands such as fatty acids, eicosanoids, and antidiabetic and antihyperlipidaemic agents. While these receptors are established as regulators of gene expression in lipid and glucose homeostasis, evidence is now accumulating that PPARs also play a crucial role in cutaneous biology. Results from in vitro and in vivo studies have indicated the involvement of PPARs in epidermal maturation, proliferation and differentiation, as well as in immune and inflammatory responses, carcinogenesis, hyperpigmentation and skin wound healing. Furthermore, treatment of psoriatic patients with PPARgamma activators (thiazolidinediones) has been shown to induce beneficial effects. However, the effects of PPAR ligands should be carefully evaluated to determine whether they are in fact mediated via PPAR-dependent mechanisms. Nonetheless, PPARs seem to have significant potential as therapeutic targets in skin inflammatory disorders.

Signal pathways underlying homocysteine-induced production of MCP-1 and IL-8 in cultured human whole blood

To elucidate the mechanisms underlying homocysteine (Hcy)-induced chemokine production. Human whole blood was pretreated with inhibitors of calmodulin (CaM), protein kinase C (PKC), protein tyrosine kinase (PTK), mitogen-activated protein kinase (MAPK), and NF-kappaB and activators of PPARgamma for 60 min followed by incubation with Hcy 100 micromol/L for 32 h. The levels of mitogen chemokine protein (MCP)-1 and interleukin-8 (IL-8) were determined by enzyme-linked immunosorbant assay (ELISA). Inhibitors of PKC (calphostin C, 50-500 nmol/L and RO-31-8220, 10-100 nmol/L), CaM (W7, 28-280 micromol/L), ERK1/2 MAPK (PD 98059, 2-20 micromol/L), p38 MAPK (SB 203580, 0.6-6 micromol/L), JNK MAPK (curcumin, 2-10 micromol/L), and NF-kappaB (PDTC, 10-100 nmol/L) markedly reduced Hcy 100 micromol/L-induced production of MCP-1 and IL-8 in human cultured whole blood, but the inhibitors of PTK (genistein, 2.6-26 micromol/L and tyrphostin, 0.5-5 micromol/L) had no obvious effect on MCP-1 and IL-8 production. PPARgamma activators (ciglitazone 30 micromol/L and troglitazone 10 micromol/L) depressed the Hcy-induced MCP-1 production but not IL-8 production in the cultured whole blood. Hcy-induced MCP-1 and IL-8 production is mediated by activated signaling pathways such as PKC, CaM, MAPK, and NF-kappaB. Our results not only provide clues for the signal transduction pathways mediating Hcy-induced chemokine production, but also offer a plausible explanation for a pathogenic role of hyperhomocysteinemia in these diseases.

Hypoglycemic Effects of Turmeric (Curcuma longa L. Rhizomes) on Genetically Diabetic KK-Ay Mice

The turmeric (Curcuma longa L. rhizomes) EtOH extract significantly suppressed an increase in blood glucose level in type 2 diabetic KK-A(y) mice. In an in vitro evaluation, the extract stimulated human adipocyte differentiation in a dose-dependent manner and showed human peroxisome proliferator-activated receptor (PPAR)-gamma ligand-binding activity in a GAL4-PPAR-gamma chimera assay. The main constituents of the extract were identified as curcumin, demethoxycurcumin, bisdemethoxycurcumin, and ar-turmerone, which had also PPAR-gamma ligand-binding activity. These results indicate that turmeric is a promising ingredient of functional food for the prevention and/or amelioration of type 2 diabetes and that curcumin, demethoxycurcumin, bisdemethoxycurcumin, and ar-turmerone mainly contribute to the effects via PPAR-gamma activation.

Prolonged treatment of genetically obese mice with conjugated linoleic acid improves glucose tolerance and lowers plasma insulin concentration: possible involvement of PPAR activation

BackgroundStudies in rodents and some studies in humans have shown that conjugated linoleic acid (CLA), especially its trans-10, cis-12 isomer, reduces body fat content. However, some but not all studies in mice and humans (though none in rats) have found that CLA promotes insulin resistance. The molecular mechanisms responsible for these effects are unclear, and there are conflicting reports on the effects of CLA on peroxisomal proliferator-activated receptor-γ (PPARγ) activation and expression. We have conducted three experiments with CLA in obese mice over three weeks, and one over eleven weeks. We have also investigated the effects of CLA isomers in PPARγ and PPARα reporter gene assays.ResultsInclusion of CLA or CLA enriched with its trans-10, cis-12 isomer in the diet of female genetically obese (lepob/lepob) mice for up to eleven weeks reduced body weight gain and white fat pad weight. After two weeks, in contrast to beneficial effects obtained with the PPARγ agonist rosiglitazone, CLA or CLA enriched with its trans-10, cis-12 isomer raised fasting blood glucose and plasma insulin concentrations, and exacerbated glucose tolerance. After 10 weeks, however, CLA had beneficial effects on glucose and insulin concentrations. At this time, CLA had no effect on the plasma TNFα concentration, but it markedly reduced the plasma adiponectin concentration. CLA and CLA enriched with either isomer raised the plasma triglyceride concentration during the first three weeks, but not subsequently. CLA enriched with its trans-10, cis-12 isomer, but not with its cis-9, trans-11 isomer, stimulated PPARγ-mediated reporter gene activity; both isomers stimulated PPARα-mediated reporter gene activity.ConclusionsCLA initially decreased but subsequently increased insulin sensitivity in lepob/lepob mice. Activation of both PPARγ and PPARα may contribute to the improvement in insulin sensitivity. In the short term, however, another mechanism, activated primarily by trans-10, cis-12-CLA, which probably leads to reduced adipocyte number and consequently reduced plasma adiponectin concentration, may decrease insulin sensitivity.

Peroxisome Proliferator-Activated Receptor-?? and its Agonists in Hypertension and Atherosclerosis

Cardiovascular diseases are the leading cause of morbidity and mortality in the US. Proper management and/or prevention of atherosclerosis and hypertension, two complex and chronic disorders, would significantly reduce the risk for cardiovascular events such as myocardial infarction and stroke, but this requires an understanding of the mechanisms underlying their development and progression. Whereas a great deal has been learned and applied toward the management of these disorders, especially hypertension, morbidity and mortality remains unacceptably high, most likely because there are disease-causing mechanisms that have yet to be fully recognized. Understanding these disease mechanisms is necessary so that novel management strategies can be developed. One of these novel mechanisms centers on peroxisome proliferator-activated receptor (PPAR)-gamma. PPAR-gamma is a member of the nuclear receptor superfamily of ligand-activated transcription factors known to play a role in glucose homeostasis and adipocyte differentiation and, more recently, has been shown to have anti-inflammatory, antiatherogenic, and antihypertensive effects. Thiazolidinediones, a class of drugs used in the treatment of type 2 diabetes mellitus, are high-affinity ligands for PPAR-gamma. In this review, the anti-inflammatory, anti-atherosclerotic, and anti-hypertensive mechanisms by which PPAR-gamma and its agonists are thought to exert protective effects on the cardiovascular system are discussed. Ongoing clinical trials using PPAR-gamma activators for the management of cardiovascular diseases, especially in patients with type 2 diabetes mellitus, are summarized.

Pharmacological profile of a novel, non‐TZD PPARγ agonist

The purpose of this study was to characterize a novel, non-thiazolidinedione (TZD) peroxisome proliferator-activated receptor (PPAR)gamma agonist, RWJ-348260, via both in vitro and in vivo approaches. The in vitro PPARgamma activities of RWJ-348260 were assessed in PPARgamma-GAL4 co-transfection assay, PPARgamma receptor binding assay, aP2 gene induction assay and preadipocyte differentiation assay. The in vivo efficacy of the compound was determined in rodent genetic diabetes models [ob/ob mouse, db/db mouse and Zucker diabetic fatty (ZDF) rat] following multiple days of oral administration. RWJ-348260 selectively activated PPARgammain vitro. In vivo, RWJ-348260 produced significant decreases in plasma glucose, HbA1c, insulin and triglyceride levels. RWJ-348260 also dose-dependently improved oral glucose tolerance. In db/db mice, the compound up-regulated PPARgamma target genes in white adipose tissues. RWJ-348260 produced a lower extent of hepatocyte lipid deposition and a smaller increase in liver weight compared to rosiglitazone in db/db mice. While RWJ-348260 effectively normalized hyperglycaemia and dyslipidaemia, it did not change haematocrit, transaminase, alkaline phosphatase, total bilirubin levels or liver weights in ZDF rats. RWJ-348260 is a potent PPARgamma agonist with efficacious antidiabetic activity in diabetic animal models. The compound has an improved side-effect profile compared to rosiglitazone.

Evaluation of adipose tissue distribution in obese fa/fa Zucker rats by in vivo MR imaging: effects of peroxisome proliferator-activated receptor agonists

High-resolution MRI of obese (fa/fa) Zucker rats was investigated to characterize and assess in vivo adipose tissue distribution. Thirty animals were gavaged with a placebo, a PPARgamma activator (pioglitazone), or a dual PPARalphagamma activator (LM 4156). At day 15, T1-weighted images were acquired in vivo using a 2TMRI system with a high in-plane spatial resolution (254 microm). Fat volumes of selected territories were measured by image segmentation, and the retroperitoneal fat was weighed post-mortem. Body-weight gain was significant with pioglitazone (101.8+/-5.9 g, p<0.01 vs. placebo). The good quality of MR images allowed the delimitation and quantification of different fat territories. In response to pioglitazone, the retroperitoneal fat was more important compared to placebo (+23%, p<0.01) while subcutaneous fat was not different. No significant effects were observed with LM 4156. In vivo measurements of fat volumes were strongly correlated with ex vivo tissue weights (r=0.91). High-resolution MRI provides an in vivo measurement of adipose tissue distribution in obese Zucker rats. Specific fat depots of regions that were particularly involved in drug response were determined in vivo. Fat remodeling was observed with pioglitazone but not with a dual PPARalphagamma activator (LM 4156).

Antidiabetic mechanisms of angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists

Several lines of evidence suggest that angiotensin-converting enzyme (ACE) inhibitors and some angiotensin II receptor blockers (ARBs) may improve insulin sensitivity and decrease the risk for type 2 diabetes. It is widely assumed that the potential antidiabetic properties of these agents are largely mediated by their ability to interfere with the adverse metabolic effects of angiotensin II. However, recent studies suggest that ACE inhibitors might improve glucose metabolism primarily through effects on kinin-nitric oxide pathways. In addition, one ARB in particular, telmisartan, has been found to effectively activate the peroxisome proliferator activated receptor gamma (PPARgamma), a well-known target for insulin-sensitizing, antidiabetic drugs. Thus, the beneficial metabolic effects of some ACE inhibitors and ARBs may go well beyond their effects on the renin-angiotensin system. Moreover, the identification of telmisartan as a unique angiotensin II receptor antagonist with selective PPARgamma modulating ability suggests new opportunities for developing third-generation ARBs and PPARgamma activators, with enhanced potential for treating hypertension, diabetes and the metabolic syndrome.

Differential inhibition of macrophage foam-cell formation and atherosclerosis in mice by PPARα, β/δ, and γ

PPARalpha, beta/delta, and gamma regulate genes involved in the control of lipid metabolism and inflammation and are expressed in all major cell types of atherosclerotic lesions. In vitro studies have suggested that PPARs exert antiatherogenic effects by inhibiting the expression of proinflammatory genes and enhancing cholesterol efflux via activation of the liver X receptor-ABCA1 (LXR-ABCA1) pathway. To investigate the potential importance of these activities in vivo, we performed a systematic analysis of the effects of PPARalpha, beta, and gamma agonists on foam-cell formation and atherosclerosis in male LDL receptor-deficient (LDLR(-/-)) mice. Like the PPARgamma agonist, a PPARalpha-specific agonist strongly inhibited atherosclerosis, whereas a PPARbeta-specific agonist failed to inhibit lesion formation. In concert with their effects on atherosclerosis, PPARalpha and PPARgamma agonists, but not the PPARbeta agonist, inhibited the formation of macrophage foam cells in the peritoneal cavity. Unexpectedly, PPARalpha and PPARgamma agonists inhibited foam-cell formation in vivo through distinct ABCA1-independent pathways. While inhibition of foam-cell formation by PPARalpha required LXRs, activation of PPARgamma reduced cholesterol esterification, induced expression of ABCG1, and stimulated HDL-dependent cholesterol efflux in an LXR-independent manner. In concert, these findings reveal receptor-specific mechanisms by which PPARs influence macrophage cholesterol homeostasis. In the future, these mechanisms may be exploited pharmacologically to inhibit the development of atherosclerosis.