Differential peroxisome proliferator-activated receptor-gamma isoform expression and agonist effects in normal and malignant prostate cells

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is being studied intensively for its role in carcinogenesis and in mediating the effects of prostate cancer treatment and prevention drugs. Prostate cancers express abundant and higher constitutive levels of PPAR-gamma than do normal prostate cells and are growth inhibited by ligand activation of PPAR-gamma. However, little is known about the role of PPARs in tumorigenesis or in normal prostate epithelial cells (EC). We examined the expression, phosphorylation patterns, and functions of the human PPAR (hPPAR)-gamma1 and hPPAR-gamma2 isoforms in normal prostate ECs to determine if activation of the receptor is sufficient for PPAR-gamma ligand activity in prostate cells. We found that ECs did not express either PPAR-gamma1 or PPAR-gamma2 protein and were not sensitive to growth inhibition by the PPAR-gamma ligand 15-deoxy-Delta12,14-prostaglandin J(2) (15d-PGJ(2)). In contrast, prostate cancer cells (PC-3), which express PPAR-gamma1 receptor isoform, are growth inhibited by PPAR-gamma ligand. Forced expression of hPPAR-gamma1 or hPPAR-gamma2 made ECs sensitive to 15d-PGJ(2) and led to reduced cellular viability. The direct repeat-1 promoter containing PPAR response elements was transactivated in ECs expressing exogenous PPAR-gamma1 or PPAR-gamma2, indicating that either isoform can be active in these cells. 15-Lipoxygenase-2, expressed at high levels in ECs, was down-regulated by transfecting PPAR-gamma expression construct (either gamma1 or gamma2 isoform) into ECs. Addition of PPAR-gamma ligand 15-hydroxyeicosatetraenoic acid in the presence of PPAR-gamma expression caused further down-regulation of 15-lipoxygenase-2. Our data illustrate that a PPAR-gamma ligand (15d-PGJ(2)) activates PPAR-gamma1 and selectively induces cell death in human prostate cancer cells but not in normal prostate ECs. These findings have important implications for the development of PPAR-gamma-targeting agents that prevent or treat prostate cancer and spare normal prostate cells.

Can PPARγ Ligands Be Used in Cancer Therapy?

The role of peroxisome-proliferator activated receptor (PPAR)gamma in tumor growth inhibition has been extensively studied during last seven years but still remains debated. Many in vitro and xenograft studies have demonstrated that PPARgamma ligands are anti-tumorigenic due to anti-proliferative, pro-differentiation and anti-angiogenic effects. In animal models, PPARgamma ligands have shown preventive effects against chemical carcinogenesis. On the other hand, evidences are accumulating against the possible use of this ligand activated nuclear receptor in molecular targeting for cancer therapy. The growth inhibitory effects of certain PPARgamma ligands have recently been shown to be independent of PPARgamma-activation. Studies have also come up with results indicating the growth promoting effects of PPARgamma-activation, particularly in certain animal models genetically predisposed to cancer development. Loss-of-function mutations of PPARgamma in tumors and increased susceptibility of PPARgamma heterozygote knockout mice to carcinogenesis suggested a tumor-suppressing role of PPARgamma. However, recent findings do not support PPARgamma as a tumor suppressor gene. Although initial clinical trials with PPARgamma ligand troglitazone reported promising results in liposarcoma and prostate cancers, recent studies failed to show the expected therapeutic values in advanced colorectal and breast cancers. In this review, we have addressed these controversies on potential use of PPARgamma ligands in cancer therapy.

Antidiabetic thiazolidinediones inhibit invasiveness of pancreatic cancer cells via PPARgamma independent mechanisms

BACKGROUND/AIMS

Thiazolidinediones (TZD) are a new class of oral antidiabetic drugs that have been shown to inhibit growth of some epithelial cancer cells. Although TZD were found to be ligands for peroxisome proliferators activated receptor gamma (PPARgamma) the mechanism by which TZD exert their anticancer effect is currently unclear. Furthermore, the effect of TZD on local motility and metastatic potential of cancer cells is unknown. The authors analysed the effects of two TZD, rosiglitazone and pioglitazone, on invasiveness of human pancreatic carcinoma cell lines in order to evaluate the potential therapeutic use of these drugs in pancreatic adenocarcinoma.

METHODS

Expression of PPARgamma in human pancreatic adenocarcinomas and pancreatic carcinoma cell lines was measured by reverse transcription polymerase chain reaction and confirmed by western blot analysis. PPARgamma activity was evaluated by transient reporter gene assay. Invasion assay was performed in modified Boyden chambers. Gelatinolytic and fibrinolytic activity were evaluated by gel zymography.

RESULTS

TZD inhibited pancreatic cancer cells' invasiveness, affecting gelatinolytic and fibrinolytic activity with a mechanism independent of PPARgamma activation and involving MMP-2 and PAI-1 expression.

CONCLUSION

TZD treatment in pancreatic cancer cells has potent inhibitory effects on growth and invasiveness suggesting that these drugs may have application for prevention and treatment of pancreatic cancer in humans.

Synthesis and antihyperglycemic activity profiles of novel thiazolidinedione derivatives

A number of thiazolidine-2,4-diones derivatives having carboxylic ester appendage at N-3 were synthesized and their antihyperglycemic activity was evaluated. Many of these derivatives as well as their corresponding carboxylic acid showed significant improvement on post-prandial hyperglycemia in normal rats, in contrast to their poor agonist activity at PPARgamma.

Fucoxanthin induces apoptosis and enhances the antiproliferative effect of the PPARγ ligand, troglitazone, on colon cancer cells

The effect of fucoxanthin, from the edible seaweed Undaria pinnatifida on viability of colon cancer cells and induction of apoptosis was investigated. Fucoxanthin remarkably reduced the viability of human colon cancer cell lines, Caco-2, HT-29 and DLD-1. Furthermore, treatment with fucoxanthin induced DNA fragmentation, indicating apoptosis. The DNA fragmentation in Caco-2 cells treated with 22.6 microM fucoxanthin for 24 h was 10-fold higher than in the control. Fucoxanthin suppressed the level of Bcl-2 protein. Also, DNA fragmentation induced by fucoxanthin was partially inhibited by a caspase inhibitor Z-VAD-fmk. Moreover, combined treatment with 3.8 microM fucoxanthin and 10 microM troglitazone, which is a specific ligand for peroxisome proliferator-activated receptor (PPAR) gamma, effectively decreased the viability of Caco-2 cells. However, separate treatments with these same concentrations of fucoxanthin nor troglitazone did not affect cell viability. These findings indicate that fucoxanthin may act as a chemopreventive and/or chemotherapeutic carotenoid in colon cancer cells by modulating cell viability in combination with troglitazone.

Pleiotropic effects of thiazolidinediones: taking a look beyond antidiabetic activity

Thiazolidinediones (TZD) [Troglitazone (TRO), Pioglitazone (PGZ), Rosiglitazone, (RGZ)] are a novel class of antidiabetic drugs for patients with Type-2 diabetes mellitus (T2DM) able to decrease blood glucose, working through a reduction of insulin resistance. The family of TZD exerts its effect specifically bound to peroxisome proliferator-activated receptor y (PPARy). This is a member of the nuclear hormone receptor superfamily of ligand-dependent transcription factors, together with PPARalpha and deltabeta. Although PPARgamma is essentially expressed in adipose tissue, it has also been found in endothelial cells, macrophages, vascular smooth muscle cells, glomerular mesangial cells, hepatic stellate cells and in several cancer cell lines. In these cells, the PPARgamma activation by TZD determines modulatory effects on growth factor release, production of cytokine, cell proliferation and migration, extracellular matrix remodeling and control on cell cycle progression and differentiation. In addition, TZD have been shown to have a potent antioxidant effect. This review, taking a quick look beyond the antidiabetic activity of PPARgamma, shows the dramatic ranging of medical implications that the use of TZD could have modulating the PPARgamma activity in several diseases with a strong social impact, such as insulin resistance syndrome, chronic inflammation, atherosclerosis and cancer.

STAT 5 activators can replace the requirement of FBS in the adipogenesis of 3T3-L1 cells

The 3T3-L1 cells differentiate into fat cells that have many properties of native adipocytes including: substantial lipid accumulation, insulin sensitivity, and the ability to secrete endocrine hormones. A substantial expense in using these cells is fetal bovine serum (FBS), a critical component of efficient adipogenesis. Our recent studies on STAT 5 proteins have revealed that these transcription factors are phosphorylated and translocate to the nucleus immediately after the initiation of differentiation. Studies by several other laboratories also suggest that STAT 5 proteins can have pro-adipogenic properties. Growth hormone (GH) and prolactin (PRL) are both potent activators of STAT 5A and STAT 5B proteins. Since, FBS has high concentrations of GH; we examined the ability of GH to replace FBS as a component of the differentiation cocktail for 3T3-L1 cells. Our studies revealed that FBS was not required for the adipogenesis of 3T3-L1 cells if GH or PRL was added to the differentiation cocktail. Adipogenesis was judged by Oil Red O staining and expression of adipocyte marker genes. Hence, we have developed a substantially less expensive method for differentiating 3T3-L1 cells without FBS, thiazolidinediones, or expensive cytokines.

Synthesis and biological activity of Benzoxazole containing thiazolidinedione derivatives

The peroxisome proliferator-activated receptors (PPARs) are a primary regulator of lipid metabolism. Potency for activation of PPARgamma, one of a subfamily of PPARs, particularly mirrors glucose lowering activity. We prepared thiazolidinediones featuring benzoxazole moiety for subtype selective PPARgamma activators. 5-[4-[2-(Benzoxazol-2-yl-alkylamino)ethoxy]benzyl]thiazolidine-2,4-diones have been prepared by Mitsunobu reaction of benzoxazolylalkylaminoethanol 8 and hydroxybenzylthiazolidinedione 6 and their activities were evaluated. Most compounds tested were identified as potent PPARgamma agonists.

Thyrotropin-producing pituitary adenoma associated with Graves' disease

OBJECTIVES

The examination of potential associations between Graves' disease and thyrotropin-producing pituitary adenoma (TSHoma) after treatment using octreotide, and of the expression of peroxisome proliferator-activated receptor gamma (PPAR gamma).

DESIGN AND METHODS

A specimen of resected TSHoma tissue from our case was immunohistochemically examined for expression of somatostatin receptor 2A (SSTR2A) and PPAR gamma. Specimens of thyroid tissue from two cases with Hashimoto's thyroiditis were immunohistochemically examined for expression of SSTR2A.

RESULTS

Expression of SSTR2A and PPAR gamma was identified in TSHoma cells. SSTR2A was also expressed in lymphocytes that had infiltrated thyroid tissue in Hashimoto's thyroiditis. In previous reports, three of four patients with TSHoma displayed Graves' disease after tumor resection, and TSH is also known to play a major role in regulating immunomodulatory gene expression in thyrocytes.

CONCLUSIONS

Both the immunomodulatory effects of octreotide on intrathyroidal lymphocytes and rapid reductions in TSH may contribute to the onset of Graves' disease. Patients with TSHoma-associated autoimmune thyroiditis should undergo careful follow-up for development of Graves' disease after treatment. Both octreotide and the PPAR gamma receptor-activating ligands, thiazolidinediones, may be effective for patients with TSHoma.

Epidermal peroxisome proliferator-activated receptor gamma as a target for ultraviolet B radiation

Ultraviolet B radiation (UVB) is a pro-oxidative stressor with profound effects on skin in part through its ability to stimulate cytokine production. Peroxisome proliferator-activated receptor gamma (PPAR gamma) has been shown to regulate inflammatory processes and cytokine release in various cell types. Since the oxidized glycerophospholipid 1-hexadecyl-2-azelaoyl glycerophosphocholine (azPC) has been shown to be a potent PPAR gamma agonist, this study was designed to assess whether the PPAR gamma system is a target for UVB irradiation and involved in UVB-induced inflammation in epidermal cells. The present studies demonstrated the presence of PPAR gamma mRNA and functional protein in human keratinocytes and epithelial cell lines HaCaT, KB, and A431. The treatment of epidermal cells with the PPAR gamma-specific agonist ciglitazone or azPC augmented cyclooxygenase-2 expression and enzyme activity induced by phorbol 12-myristate-13-acetate or interleukin-1 beta. Lipid extracts from the cell homogenate of UVB-irradiated, but not control, cells contained a PPAR gamma-agonistic activity identified by reporter assay, and this activity up-regulated cyclooxygenase-2 expression induced by phorbol 12-myristate-13-acetate. Subjecting purified 1-hexadecyl-2-arachidonoyl-glycerophosphocholine to UVB irradiation generated a PPAR gamma-agonistic activity, among which the specific PPAR gamma agonist azPC was identified by mass spectrometry. These findings suggested that UVB-generated PPAR gamma-agonistic activity was due to the free radical mediated non-enzymatic cleavage of endogenous glycerophosphocholines. Treatment with the specific PPAR gamma antagonist GW9662 or expression of a dominant-negative PPAR gamma mutant in KB cells inhibited UVB-induced epidermal cell prostaglandin E(2) production. These findings suggested that UVB-generated PPAR gamma activity is necessary for the optimal production of epidermal prostaglandins. These studies demonstrated that epithelial cells contain a functional PPAR gamma system, and this system is a target for UVB through the production of novel oxidatively modified endogenous phospholipids.

Serum adiponectin as a biomarker for in vivo PPARgamma activation and PPARgamma agonist-induced efficacy on insulin sensitization/lipid lowering in rats

Background

PPARγ agonists ameliorate insulin resistance and dyslipidemia in type 2 diabetic patients. Adiponectin possesses insulin sensitizing properties, and predicts insulin sensitivity of both glucose and lipid metabolism. In diet-induced insulin resistant rats and ZDF rats, the current studies determined the correlation between PPARγ agonist-upregulated fatty acid binding protein(FABP3) mRNA in adipose tissue and PPARγ agonist-elevated serum adiponectin, and the correlation between PPARγ agonist-elevated serum adiponectin and PPARγ agonist-mediated efficacy in insulin sensitization and lipid lowering.

Results

Parallel groups of SD rats were fed a high fat/sucrose (HF) diet for 4 weeks. These rats were orally treated for the later 2 weeks with vehicle, either PPARγ agonist GI262570 (0.2–100 mg/kg, Q.D.), or GW347845 (3 mg/kg, B.I.D). Rats on HF diet showed significant increases in postprandial serum triglycerides, free fatty acids (FFA), insulin, and area under curve (AUC) of serum insulin during an oral glucose tolerance test, but showed no change in serum glucose, adiponectin, and glucose AUC. Treatment with GI262570 dose-dependently upregulated adipose FABP3 mRNA, and increased serum adiponectin. There was a positive correlation between adipose FABP3 mRNA and serum adiponectin (r = 0.7350, p < 0.01). GI262570 dose-dependently decreased the diet-induced elevations in triglycerides, FFA, insulin, and insulin AUC. Treatment with GW347845 had similar effects on serum adiponectin and the diet-induced elevations. There were negative correlations for adiponectin versus triglycerides, FFA, insulin, and insulin AUC (For GI262570, r = -0.7486, -0.4581, -0.4379, and -0.3258 respectively, all p < 0.05. For GW347845, r = -0.6370, -0.6877, -0.5512, and -0.3812 respectively, all p < 0.05). In ZDF rats treated with PPARγ agonists pioglitazone (3–30 mg/kg, B.I.D.) or GW347845 (3 mg/kg, B.I.D.), there were also negative correlations for serum adiponectin versus glucose, triglycerides, FFA (for pioglitazone, r = -0.7005, -0.8603, and -0.9288 respectively; for GW347845, r = -0.9721, -0.8483, and -0.9453 respectively, all p < 0.01).

Conclusions

This study demonstrated that (a) PPARγ agonists improved insulin sensitivity and ameliorated dyslipidemia in HF fed rats and ZDF rats, which were correlated with serum adiponectin; (b) Serum adiponectin was positively correlated with adipose FABP3 mRNA in GI262570-treated rats. These data suggest that serum adiponectin can serve as a biomarker for both in vivo PPARγ activation and PPARγ agonist-induced efficacy on insulin resistance and dyslipidemia in rats.

Treatment of active psoriatic arthritis with the PPARgamma ligand pioglitazone: an open-label pilot study

OBJECTIVES

Psoriatic arthritis (PsA) is an inflammatory joint disease, in which early neovascularization of affected skin and synovial tissue represents an important pathogenetic step in the disease process. Activation of the peroxisome proliferator activated receptor gamma (PPARgamma) showed anti-inflammatory effects in several in vitro and in vivo models (e.g. collagen-induced arthritis) by inhibition of angiogenesis and suppression of proinflammatory cytokines. Therefore, we studied the use of pioglitazone, a PPARgamma agonist originally developed for the treatment of diabetes, in patients with PsA.

METHODS

Ten patients with active PsA, seven males and three females, who showed at least two tender and two swollen joints despite stable treatment with an NSAID, were enrolled in this open-label study. All patients received a daily dose of 60 mg pioglitazone while continuing their current NSAID therapy. The primary endpoint was the PsARC (Psoriatic Arthritis Response Criterion); the secondary endpoints included the ACR20 response and improvement in the Psoriasis Area and Severity Index (PASI) in patients with more than 2% skin involvement. Patients were evaluated for endpoints at baseline and after 12 weeks.

RESULTS

After 12 weeks, six of 10 patients met the PsARC. The ACR20 response was achieved in five patients. The mean percentage reduction in PASI was 38%, with a clinically meaningful PASI 50 response in two of six patients. Median tender joint count (interquartile range) decreased from 12.0 (8.0-18.0) to 4.0 (2.0-10.0), and the median swollen joint count from 5.0 (4.0-8.0) to 2.0 (1.0-7.0) (P<0.05 for both). Median Health Assessment Questionnaire score changed from 1.0 (0.375-1.375) to 0.75 (0.375-1.0) (P<0.05). Three patients had to be withdrawn from the study due to inefficacy and side-effects. Major side-effects were oedema of the lower extremities and increase in weight.

CONCLUSIONS

Treatment with a PPARgamma agonist appears to be a promising therapeutic principle in PsA, but the use of PPARgamma ligands might be limited by side-effects such as increase in weight and fluid retention.

Peroxisome proliferator-activated receptor gamma ligands improve the antitumor efficacy of thrombospondin peptide ABT510

An expanding capillary network is critical for several pathologic conditions. In cancer, the decrease of antiangiogenic thrombospondin-1 (TSP1) often enables an angiogenic switch, which can be reversed with exogenous TSP1 or its peptide derivative ABT510. TSP1 acts by inducing endothelial cell apoptosis via signaling cascade initiated at CD36, a TSP1 antiangiogenic receptor. Here, we show that the ligands of nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma), 15-deoxy-delta(12,14)-prostaglandin J2, troglitazone, and rosiglitazone increased PPARgamma and CD36 expression in endothelial cells and improved the efficacy of TSP1 and ABT510 in a CD36-dependent manner. The ABT510 and PPARgamma ligands cooperatively blocked angiogenic endothelial functions in vitro and neovascularization in vivo. In tumor xenografts, 15-deoxy-delta(12,14)-prostaglandin J2 and troglitazone synergistically improved antiangiogenic and antitumor effects of ABT510. Our data provide one mechanism for the in vivo angioinhibitory effect of PPARgamma ligands and show fine-tuning of the antiangiogenic efficacy via targeted up-regulation of the endothelial receptor.

Insulin resistance and cardiovascular disease: the role of PPARgamma activators beyond their anti-diabetic action

Over the past few years it has been recognised that insulin resistance (IR) is an independent risk factor for major cardiovascular events. In addition, IR is associated with other factors such as hypertension, dyslipidaemia and endothelial dysfunction, and this cluster of metabolic disorders contributes to the cardiovascular risk of patients with IR. Given the increasing number of patients with IR, the modulation of their cardiovascular risk is a major task in diabetology and vascular medicine. This review will focus on the role of IR as a cardiovascular risk factor and on the potential of activators of the nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) to modulate these risk factors associated with IR.

Enhanced marrow adipogenesis and bone resorption in estrogen-deprived rats treated with the PPARgamma agonist BRL49653 (rosiglitazone)

Thiazolidinediones are insulin-sensitizing agents and in clinical use for the treatment of type II diabetes. Under specific experimental conditions, these molecules induce adipogenic differentiation of mesenchymal precursor cells at the expense of osteoblasts in vitro, suggesting possible negative effects on the skeleton. We measured effects of the thiazolidinedione BRL49653 on bone tissue of intact and estrogen-deprived skeletally mature adult female Wistar rats (6-9 months old). Weight gain and decreased plasma triglyceride levels confirmed the effectiveness of the treatment. However, no change in bone mass or fat marrow volume was observed in intact rats treated for 8 weeks with 5, 10, or 20 mg/kg of BRL49653. Study of marrow cultures established at necropsy revealed a higher responsiveness to adipogenic differentiation protocols of cultures established from the 10-mg/kg group compared to vehicle control. In a second study, the effects of thiazolidinedione treatment on the skeleton of estrogen-deprived rats were investigated. Application of 10 mg/kg of BRL49653 for 12 weeks resulted in enhanced bone loss (+31%; pQCT) and increased fat marrow volume (+117%; histomorphometry) compared to vehicle-treated OVX control. Interestingly, osteoblast number was comparable in both cases. Bone resorption parameters were significantly increased in the treatment group (+27% osteoclast number, +30% eroded surface). Enhanced bone loss due to treatment was consistently observed in the tibia, femur, and the lumbar spine. Our data indicate that thiazolidinediones may enhance bone loss induced by estrogen deprivation.

Peroxisome proliferator-activated receptor gamma and retinoid X receptor ligands are potent inducers of differentiation and apoptosis in leukemias

The peroxisome proliferator-activated receptor gamma (PPAR gamma) is a member of the nuclear receptor family that forms heterodimers with retinoid X receptor. These heterodimers bind to DNA and activate the transcription of target genes. Here, we report that the PPAR gamma receptor protein is expressed in primary myeloid and lymphoid leukemias and in lymphoma and myeloma cell lines. In this study, we compared the activity of several PPAR gamma ligands including BRL49653 (rosiglitazone), 15-deoxy-Delta 12,14-prostaglandin J(2), and the novel triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid on leukemia cells. Exposure to these PPAR gamma ligands induced apoptosis in myeloid (U937 and HL-60) and lymphoid (Su-DHL, Sup-M2, Ramos, Raji, Hodgkin's cell lines, and primary chronic lymphocytic leukemia) cells. A similar exposure to these PPAR gamma ligands induced the differentiation of myeloid leukemic cells. A combination of PPAR gamma ligands with a retinoid X receptor agonist (i.e., LG100268) or a retinoic acid receptor agonist (i.e., all trans-retinoic acid) enhanced differentiating and growth-inhibitory effects. 2-Cyano-3,12-dioxooleana-1,9-dien-28-oic acid induced differentiation and apoptosis with much greater potency than the other PPAR gamma ligands in established cell lines and primary chronic lymphocytic leukemia samples. Exposure to 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid induced mitochondrial depolarization and caspase activation, which was associated with apoptosis induction. In Bcl-2-overexpressing chronic lymphocytic leukemia cells, the small-molecule Bcl-2 inhibitor HA14-1 sensitized these cells to 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid-induced apoptosis. These results suggest that PPAR gamma ligation alone and in combination with retinoids holds promise as novel therapy for leukemias by activating the transcriptional activity of target genes that control apoptosis and differentiation in leukemias.

A novel PPAR alpha/gamma dual agonist inhibits cell growth and induces apoptosis in human glioblastoma T98G cells

AIM

To examine the effect of a novel peroxisome proliferator-activated receptor (PPAR) alpha/gamma dual agonist TZD18 on cell proliferation and apoptosis in human glioblastoma T98G cells and its possible mechanism.

METHODS

RT-PCR, MTT, TUNEL, Flow cytometry, and Western blot analysis were employed.

RESULTS

TZD18 inhibited the growth of T98G cells in a concentration-dependent manner, which was associated with a G1 to S cell cycle arrest. Besides, significant apoptosis was induced after treatment with a non-toxic dose of TZD18. During the process, the expression of Bcl-2 protein was down-regulated, while that of Bax and p27kip proteins was up-regulated, and the activity of caspase-3 was elevated. However, this effect appeared to be PPARalpha and PPARgamma independent since their antagonists could not reverse this effect.

CONCLUSIONS

TZD18, a novel PPARalpha/gamma dual agonist, inhibited cell growth and induce apoptosis in human glioblastoma T98G cells in vitro, indicating a therapeutic potential for TZD18 in the treatment of glioblastoma.

Potency of arachidonic acid in polyunsaturated fatty acid-induced death of human monocyte-macrophages: implications for atherosclerosis

Evidence suggests that oxidation of LDL is involved in the progression of atherosclerosis by inducing apoptosis in macrophages. Polyunsaturated fatty acids (PUFAs) are prominent components of LDL and are highly peroxidisable. We therefore tested PUFAs for induction of apoptosis in human monocyte-macrophages in vitro. Arachidonic acid (AA) induced the highest levels of apoptosis followed by docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), despite DHA and EPA being more peroxidisable than AA. alpha-Linolenic acid induced lower levels of apoptosis. Linoleic and oleic acids were innocuous. Results of experiments with AA products and enzyme inhibitors suggest roles for peroxidation, cyclooxygenase and lipoxygenase in AA-induced apoptosis. Our results further suggest activation of PPARgamma by AA and DHA associated with apoptosis induction. These findings may be relevant to potential mechanisms of fatty acid influences on plaques and may suggest strategies for combating atherosclerosis progression.

Ligand-independent activation of peroxisome proliferator-activated receptor-gamma by insulin and C-peptide in kidney proximal tubular cells: dependent on phosphatidylinositol 3-kinase activity

Peroxisome proliferator-activated receptor gamma (PPARgamma) has key roles in the regulation of adipogenesis, inflammation, and lipid and glucose metabolism. C-peptide is believed to be inert and without appreciable biological functions. Recent studies suggest that C-peptide possesses multiple functions. The present study investigated the effects of insulin and C-peptide on PPARgamma transcriptional activity in opossum kidney proximal tubular cells. Both insulin and C-peptide induced a concentration-dependent stimulation of PPARgamma transcriptional activity. Both agents substantially augmented thiazolidinedione-stimulated PPARgamma transcriptional activity. Neither insulin nor C-peptide had any effect on the expression levels of PPARgamma. GW9662, a PPARgamma antagonist, blocked PPARgamma activation by thiazolidinediones but had no effect on either insulin- or C-peptide-stimulated PPARgamma transcriptional activity. Co-transfection of opossum kidney cells with dominant negative mitogen-activated protein kinase kinase significantly depressed basal PPARgamma transcriptional activity but had no effect on that induced by either insulin or C-peptide. Both insulin- and C-peptide-stimulated PPARgamma transcriptional activity were attenuated by wortmannin and by expression of a dominant negative phosphatidylinositol (PI) 3-kinase p85 regulatory subunit. In addition PI 3-kinase-dependent phosphorylation of PPARgamma was observed after stimulation by C-peptide or insulin. C-peptide effects but not insulin on PPARgamma transcriptional activity were abolished by pertussis toxin pretreatment. Finally both C-peptide and insulin positively control the expression of the PPARgamma-regulated CD36 scavenger receptor in human THP-1 monocytes. We concluded that insulin and C-peptide can stimulate PPARgamma activity in a ligand-independent fashion and that this effect is mediated by PI 3-kinase. These results support a new and potentially important physiological role for C-peptide in regulation of PPARgamma-related cell functions.

Enhanced bone formation in lipodystrophic PPARgamma(hyp/hyp) mice relocates haematopoiesis to the spleen

The peroxisome proliferator-activated receptor gamma (PPARgamma) controls adipogenesis and metabolism. We demonstrate here that the absence of PPARgamma in fat has potent osteogenic activities, which affect haematopoiesis. The congenital absence of PPARgamma in fat of lipodystrophic PPARgamma(hyp/hyp) mice, strongly enhanced bone mass and consequentially reduced the bone-marrow cavity. Consistent with this, PPARgamma(hyp/hyp) mice had a significant decrease in bone marrow cellularity and resorted to extramedullary haematopoiesis in the spleen to maintain haematopoiesis. Our data indicate that antagonizing PPARgamma activity in fat could be an effective way to combat osteoporosis and suggest that haematopoietic function should be scrutinized in lipodystrophic subjects.

The PAX8 / PPARγ Fusion Oncogene as a Potential Therapeutic Target in Follicular Thyroid Carcinoma

Follicular thyroid carcinoma (FTC) accounts for approximately 20% of all thyroid cancers, and up to 40% of the deaths associated with this disease. Current treatment approaches include surgery, followed by radioactive iodine therapy. However, a significant proportion of locally advanced and metastatic FTC fails to concentrate iodine. Because traditional chemotherapeutic agents have not been shown to alter outcomes in this disease, novel therapeutic strategies are needed for advanced disease. Recently, a genomic rearrangement has been identified in up to 50% of FTC, involving a translocation event between chromosome regions 3p25 and 2q13. This translocation fuses the thyroid-specific transcription factor PAX8 gene with the PPARgamma gene, a ubiquitously expressed transcription factor. We have confirmed that this Pax8/PPARgamma fusion gene (designated PPFP) is an oncogene, which accelerates cell growth, reduces rates of apoptosis and permits anchorage independent and contact uninhibited growth of a thyroid cell line. The action of PPFP arises, at least in part, through its activity as a dominant-negative inhibitor of the wild-type PPARgamma transcription factor. Although the mechanism by which PPFP impairs PPARgamma activity remains unknown at this time, it is likely to be mediated by competition for the genomic PPARgamma response elements, the endogenous ligand, or various cofactors, including the Retinoid X Receptor (RXR). Consequently, modulation of PPFP activity might be possible through the use of PPARgamma agonists, RXR-agonists, or specific modulators of PPFP itself. Alternatively, modulation of several down-stream regulatory pathways may become possible, as the consequences of PPARgamma inhibition become better known. PPFP represents a potential novel target for the management of advanced FTC.

Beneficial and deleterious effects of rosiglitazone on hypertension development in spontaneously hypertensive rats

The antihypertensive effect of the peroxisome proliferator-activated receptor (PPAR)gamma agonist rosiglitazone has been reported in patients with diabetes or obesity. The correlation of PPARgamma expression with blood pressure and the therapeutic application of rosiglitazone in spontaneously hypertensive rats (SHR) were investigated in the present study. Systolic blood pressure of 21-week SHR was significantly higher than that of age-matched Wistar-Kyoto rats (WKY) (225 +/- 5 v 144 +/- 2 mm Hg, P <.05). Basal expression levels of PPARgamma proteins in vascular tissues of 21-week SHR were significantly lower than that of age-matched 21-week WKY (P <.05). This reduced expression of PPARgamma was not detected between 5- and 13- week SHR and age-matched WKY. Cardiac PPARgamma expression was also not different among different age groups between SHR and WKY. Chronic treatment with rosiglitazone, but not PPARalpha agonist Wy14643, significantly retarded hypertension development and reversed abnormally faster heart rate in young SHR. An unfavorable effect of rosiglitazone treatment was the increased heart-to-body weight ratio accompanied by left ventricular hypertrophy. In conclusion, vascular PPARgamma protein expression in adult SHR (21 weeks) is significantly decreased in comparison with the age-matched WKY. Chronic rosiglitazone treatment retards hypertension development, but the associated prohypertrophy effect calls for a cautious use of this thiazolidinedindione in the treatment of insulin resistance syndrome associated with hypertension.

[Ciglitazone inhibits growth of lung cancer cells A549 in vitro and in vivo: an experimental study]

OBJECTIVE

To study the inhibitory effects of ciglitazone, a synthetic ligand of peroxisome proliferator-activated receptors (PPAR), on human lung cancer growth in vitro and in vivo and its mechanisms.

METHODS

Human lung cancer A549 cells cultured in vitro were treated with different concentrations of ciglitazone. The proliferative activity and cell cycle of A549 cells were determined by MTT assay and flow cytometry. Expression of PPARgamma protein was detected by Western blot. A549 cells (1 x 10(6) cells/nude mouse) were inoculated subcutaneously into nude mice, which were randomly divided into two groups, 10 in each: control group (group A) and ciglitazone treated group (group B). When the tumors grew to a size with diameter around 1 cm, ciglitazone 100 microl (100 micromol/L) was intratumorally injected every other day in group B mice. A total of 15 injections were given. Mice in group A were similarly treated with normal saline. One month later, tumors were excised and weighed. Expression of cyclin D1 and p21 protein were detected by immunohistochemistry and Western blot.

RESULTS

Growth of A549 cells was significantly inhibited in group B in a dose-dependent and time-dependent fashion as compared with that in group A. Most of the ciglitazone-treated cells arrested in G(1)/G(0) phase and the expression of PPARgamma protein was markedly up-regulated. The tumor weights in group A was (2.79 +/- 0.33) g and that in group B was (1.51 +/- 0.40) g, with an inhibition rate of 47.0%. The expression level of cyclin D1 in group A was significantly higher than that in group B, while the expression level of p21 protein in group A was significantly lower than that in group B.

CONCLUSION

Ciglitazone can effectively inhibit the growth of human lung cancer A549 and induce its differentiation by cell cycle arrest via PPARgamma activation.

Effects of cardiotrophin on adipocytes

Cardiotrophin (CT-1) is a naturally occurring protein member of the interleukin (IL)-6 cytokine family and signals through the gp130/leukemia inhibitory factor receptor (LIFR) heterodimer. The formation of gp130/LIFR complex triggers the auto/trans-phosphorylation of associated Janus kinases, leading to the activation of Janus kinase/STAT and MAPK (ERK1 and -2) signaling pathways. Since adipocytes express both gp130 and LIFR proteins and are responsive to other IL-6 family cytokines, we examined the effects of CT-1 on 3T3-L1 adipocytes. Our studies have shown that CT-1 administration results in a dose- and time-dependent activation and nuclear translocation of STAT1, -3, -5A, and -5B as well as ERK1 and -2. We also confirmed the ability of CT-1 to induce signaling in fat cells in vivo. Our studies revealed that neither CT-1 nor ciliary neurotrophic factor treatment affected adipocyte differentiation. However, acute CT-1 treatment caused an increase in SOCS-3 mRNA in adipocytes and a transient decrease in peroxisome proliferator-activated receptor gamma (PPARgamma) mRNA that was regulated by the binding of STAT1 to the PPARgamma2 promoter. The effects of CT-1 on SOCS-3 and PPARgamma mRNA were independent of MAPK activation. Chronic administration of CT-1 to 3T3-L1 adipocytes resulted in a decrease of both fatty acid synthase and insulin receptor substrate-1 protein expression yet did not effect the expression of a variety of other adipocyte proteins. Moreover, chronic CT-1 treatment resulted in the development of insulin resistance as judged by a decrease in insulin-stimulated glucose uptake. In summary, CT-1 is a potent regulator of signaling in adipocytes in vitro and in vivo, and our current efforts are focused on determining the role of this cardioprotective cytokine on adipocyte physiology.

Divergent effects of peroxisome proliferator-activated receptor gamma agonists and tumor necrosis factor alpha on adipocyte ApoE expression

ApoE is expressed in multiple mammalian cell types in which it supports cellular differentiated function. In this report we demonstrate that apoE expression in adipocytes is regulated by factors involved in modulating systemic insulin sensitivity. Systemic treatment with pioglitazone increased systemic insulin sensitivity and increased apoE mRNA levels in adipose tissue by 2-3-fold. Treatment of cultured 3T3-L1 adipocytes with ciglitazone increased apoE mRNA levels by 2-4-fold in a dose-dependent manner and increased apoE secretion from cells. Conversely, treatment of adipocytes with tumor necrosis factor (TNF) alpha reduced apoE mRNA levels and apoE secretion by 60%. Neither insulin nor a peroxisome proliferator-activated receptor (PPAR) alpha agonist regulated adipocyte apoE gene expression. In addition, treatment of human monocyte-derived macrophages with ciglitazone did not regulate expression of apoE. Additional analyses using reporter genes indicated that the effect of TNFalpha and PPARgamma agonists on the apoE gene was mediated via distinct gene control elements. The TNFalpha effect was mediated by elements within the proximal promoter, whereas the PPARgamma effect was mediated by elements within a downstream enhancer. However, the addition of TNFalpha substantially reduced the absolute levels of apoE reporter gene response even in the presence of ciglitazone. These results indicate for the first time that adipose tissue expression of apoE is modulated by physiologic regulators of insulin sensitivity.

Cytosolic phospholipase A2 Group IValpha but not secreted phospholipase A2 Group IIA, V, or X induces interleukin-8 and cyclooxygenase-2 gene and protein expression through peroxisome proliferator-activated receptors gamma 1 and 2 in human lung cells

It has been reported that interleukin-8 (IL-8) and cyclooxygenase-2 (COX-2) expression is regulated by peroxisome proliferator-activated receptor (PPAR)-gamma synthetic ligands. We have shown previously that cytosolic phospholipase A2 (cPLA2) is able to activate gene expression through PPAR-gamma response elements (Pawliczak, R., Han, C., Huang, X. L., Demetris, A. J., Shelhamer, J. H., and Wu, T. (2002) J. Biol. Chem. 277, 33153-33163). In this study we investigated the influence of cPLA2 and secreted phospholipase A2 (sPLA2) Group IIA, Group V, and Group X on IL-8 and COX-2 expression in human lung epithelial cells (A549 cells). We also studied the results of cPLA2 activation by epidermal growth factor (EGF) and calcium ionophore (A23187) on IL-8 and COX-2 reporter gene activity, mRNA level, and protein synthesis. cPLA2 overexpression and activation increased both IL-8 and COX-2 reporter gene activity. Overexpression and activation of Group IIA, Group V, or Group X sPLA2s did not increase IL-8 and COX-2 reporter gene activity. Methyl arachidonyl fluorophosphate, a cPLA2 inhibitor, inhibited the effect of A23187 and of EGF on both IL-8 and COX-2 reporter gene activity, steady state levels of IL-8 and COX-2 mRNA, and IL-8 and COX-2 protein expression. Small inhibitory RNAs directed against PPAR-gamma1 and -gamma2 blunted the effect of A23187 and of EGF on IL-8 and COX-2 protein expression. Moreover small inhibitory RNAs directed against cPLA2 decreased the effect of A23187 and EGF on IL-8 and COX-2 protein expression. These results demonstrate that cPLA2 has an influence on IL-8 and COX 2 gene and protein expression at least in part through PPAR-gamma.

Transforming growth factor-beta (TGF-beta) activates cytosolic phospholipase A2alpha (cPLA2alpha)-mediated prostaglandin E2 (PGE)2/EP1 and peroxisome proliferator-activated receptor-gamma (PPAR-gamma)/Smad signaling pathways in human liver cancer cells. A novel mechanism for subversion of TGF-beta-induced mitoinhibition

Transforming growth factor-beta (TGF-beta) potently inhibits the growth of human epithelial cells. However, neoplastic epithelial cells become resistant to TGF-beta-mediated mitoinhibition, and the mechanisms for this alteration during tumorigenesis are not fully understood. This study was designed to determine whether there is an association between the cytosolic phospholipase A2alpha (cPLA2alpha)-controlled eicosanoid metabolism and the growth response to TGF-beta in human liver cancer cells. TGF-beta treatment induced simultaneous Smad-mediated gene transcription and phosphorylation of cPLA2alpha. Whereas Smad activation inhibited tumor cell growth, phosphorylation of cPLA2 alpha promoted growth and counteracted Smad-mediated mitoinhibition. TGF-beta1 failed to prevent the growth of cells with high basal expression of cPLA2alpha, but inhibition of cPLA2 alpha, cyclooxygenase-2 (COX-2), or EP1 receptor restored mitoinhibition by TGF-beta1 in these cells. These results suggest that resistance of tumor cells to TGF-beta-mediated mitoinhibition involves activation of cPLA2alpha/COX-2/EP1 signaling. Furthermore, the TGF-beta1-induced Smad transcriptional activity and mitoinhibition were blocked by overexpression of cPLA2alpha or peroxisome proliferator-activated receptor-gamma (PPAR-gamma) but enhanced by depletion of cPLA2alpha or PPAR-gamma. These findings, along with the observations that cPLA2alpha activates PPAR-gamma and that PPAR-gamma binds Smad3, illustrate novel cPLA2alpha/COX-2/EP1 and cPLA2alpha/PPAR-gamma/Smad signaling pathways that counteract the mitoinhibition by TGF-beta in human cancer cells.

Transcriptome analysis of endometrial cancer identifies peroxisome proliferator-activated receptors as potential therapeutic targets

Endometrial cancer is the most common gynecologic malignancy, frequently arising in association with obesity and diabetes mellitus. To identify gene pathways contributing to endometrial cancer development, we studied the transcriptome of 20 endometrial cancers and 11 benign endometrial tissues using cDNA microarrays. Among the transcript changes identified in endometrial cancer were up-regulation of the nuclear hormone receptors peroxisome proliferator-activated receptors (PPAR) alpha and gamma, whereas retinoid X receptor beta was down-regulated. To clarify the contribution of PPARalpha to endometrial carcinogenesis, we did experiments on cultured endometrial carcinoma cells expressing this transcript. Treatment with fenofibrate, an activating ligand for PPARalpha, significantly reduced proliferation and increased cell death, suggesting that altered expression of nuclear hormone receptors involved with fatty acid metabolism leads to deregulated cellular proliferation and apoptosis. These results support further investigation of members of the PPAR/retinoid X receptor pathway as novel therapeutic targets in endometrial cancer.

The localisation and reduction of nuclear staining of PPARgamma and PGC-1 in human breast cancer

Peroxisome proliferator activated receptor-gamma (PPARgamma) belongs to a family of nuclear receptors and acts as a receptor for peroxisome proliferators, steroids, retinoic acids and polyunsaturated fatty acids. The current study examined both the transcript levels of PPARgamma and its coactivator PGC-1, and the localisation of these molecules in breast cancer tissues. Both PPARgamma and PGC-1 were located exclusively within the nucleus of epithelium and breast cancer tissues. Nuclear staining of both molecules was weaker in cancer cells compared with normal mammary epithelium. Computerised image analysis was used to quantify the immunohistochemical staining intensity, and this demonstrated that normal back-ground breast tissue exhibited higher levels of both PPARgamma (mean +/- sd, 4.57+/-1.03) and PGC-1 (2.84+/-0.64), respectively. In contrast, tumour tissue exhibited significantly lower levels of PPARgamma (1.45+/-0.74, p<0.001 versus normal background tissue) and for PGC-1 (1.23+/-0.60, p<0.001 versus normal background tissue). This study also showed a variation in the levels of PGC-1 and PPARgamma between ductal and lobular tumours. These findings were corroborated by mRNA analysis which also demonstrated lower levels of both PGC-1 and PPARgamma in breast tumour tissue. It is concluded that both PPARgamma and its coactivator PGC-1 play important roles in the development and progression of breast cancer, and may have a significant bearing on patient prognosis.

Mitochondrial Dysfunction by Synthetic Ligands of Peroxisome Proliferator Activated Receptors (PPARs)

PPARs are a class of nuclear receptors involved in lipid and glucidic metabolism, immune regulation and cell differentiation. This spectrum of biological activities stimulated pharmacological research to synthetize different molecules with PPARs binding activity with beneficial therapeutic effects. As a matter of fact, some synthetic PPAR-ligands have been already employed in pharmacotherapy: PPAR-alpha ligands, such as fibrates, are used in hyperlipidemias and thiazolidinediones, mainly PPAR-gamma ligands, are employed as insulin sensitizers. However, both classes of drugs showed pharmacotoxicological profiles which cannot be fully ascribed to activation of their specific receptors and which are causing a growing incidence of dramatic side effects (rhabdomyolysis, acute liver failure, heart failure, etc.). A re-evaluation of the biological activities of PPAR synthetic ligands, in particular of the mitochondrial dysfunction based on a rotenone-like Complex I partial inhibition and of its consequent metabolic adaptations, seems to explain some of the pathophysiologic aspects of PPARs allowing a better definition of the therapeutic properties of the so-called PPAR-ligands.

Human adipocyte fatty acid-binding protein (aP2) gene promoter-driven reporter assay discriminates nonlipogenic peroxisome proliferator-activated receptor gamma ligands

Peroxisome proliferator-activated receptors (PPARs) regulate storage and catabolism of fats and carbohydrates. PPARgamma activity increases insulin sensitivity and adipocyte differentiation at the expense of adipogenesis and weight gain. The goal of this study was to 1) clone the promoter of the human adipocyte fatty acid binding protein (aP2) gene, namely fatty acid-binding protein-4, 2) characterize its pharmacological regulation, and 3) determine its putative predictability for adipogenesis. Among the selected PPAR agonists, rosiglitazone and pioglitazone displayed the highest maximal efficacy (E(max)) on reporter-gene assays in COS-7 cells cotransfected by either a galactosidase 4-response element-based or a human aP2 promoter-based Luc reporter vector, along with either chimeric or full-length human PPAR expression plasmids. The non-subtype-selective 2-(4-[2-(3-[2,4-difluorophenyl]-1-heptylureido)ethyl]phenoxy)-2-methyl-butyric acid (GW-2331) and the compounds [4-[3-(4-acetyl-3-hydroxy-2-propylphenoxy)-propoxyl]phenoxy]-acetic acid (L-165041), (4-((2S,5S)-5-(2-(bis(phenylmethyl)amino)-2-oxoethyl)-2-heptyl-4-oxo-3-thiazolidinyl)butyl)-benzoic acid (GW-0072), and indomethacin behaved as partial agonists relative to pioglitazone in full-length human aP2-PPARgamma2. Beyond their partial PPARgamma agonist properties, these compounds elicited a lower maximal up-regulation of mouse aP2 mRNA in 3T3-L1 adipocytes as compared with pioglitazone; these properties paralleled a time-dependent increase in neutral lipids. By contrast, the selective PPARalpha agonist 2,2-dichloro-12-(4-chlorophenyl)dodecanoic acid (BM-17.0744) neither stimulated the human aP2-PPARalpha promoter reporter-gene assay, thus demonstrating a specific interaction between PPARgamma and the aP2 promoter, nor affected lipogenesis in 3T3-L1 cells. Altogether, these data characterized a functional promoter of the human aP2 gene; its in vitro pharmacological regulation in PPARgamma-mediated reporter-gene assay may represent an interesting complement or an alternative to time-consuming procedures aiming at discriminating PPAR ligands with low lipogenic properties.

The forkhead transcription factor FoxC2 inhibits white adipocyte differentiation

In this study, we show that expression of FoxC2 blocks the capacity of 3T3-L1 preadipocytes to undergo adipogenesis in the presence of dexamethasone, isobutylmethylxanthine, and insulin. This block is characterized by an extensive decrease in the expression of proteins associated with the function of the mature fat cell, most notably C/EBPalpha, adiponectin, perilipin, and the adipose-specific fatty acid-binding protein, FABP4/aP2. Since the expression of these proteins lies downstream of PPARgamma, we overexpressed PPARgamma in Swiss mouse fibroblasts to promote adipocyte differentiation. We show that FoxC2 blocks the ability of PPARgamma to induce adipogenic gene expression in response to exposure of the cells to dexamethasone, isobutylmethylxanthine, insulin, and a PPARgamma ligand. Interestingly, the expression of aP2 escapes the inhibitory action of FoxC2 under conditions that promote maximum PPARgamma activity. In contrast, FoxC2 inhibits the expression of C/EBPalpha, perilipin, and adiponectin even in the presence of potent PPARgamma ligands. Finally, we show that FoxC2 does not affect the ability of PPARgamma to bind to or transactivate from a PPARgamma response element. These data suggest that FoxC2 blocks adipogenesis by inhibiting the capacity of PPARgamma to promote the expression of a subset of adipogenic genes.

Proinflammatory cytokines regulate LOX-1 expression in vascular smooth muscle cells

OBJECTIVE

Atherogenesis represents a type of chronic inflammation and involves elements of the immune response, eg, the expression of proinflammatory cytokines. In advanced atherosclerotic lesions, lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is expressed in endothelial cells, macrophages, and smooth muscle cells (SMCs). In vitro, the expression of LOX-1 is induced by inflammatory cytokines like TNF-alpha and transforming growth factor (TGF)-beta. Therefore, LOX-1 is thought to be upregulated locally in response to cytokines in vivo.

METHODS AND RESULTS

We determined by reverse-transcription polymerase chain reaction (PCR) and Western blot analysis whether the mediators of the acute phase response in inflammation, IL-1alpha, IL-1beta, and TNF-alpha, regulate LOX-1 expression in cultured SMC, and whether this regulation is influenced by peroxisome proliferator-activated receptor gamma (PPARgamma). We studied by immunohistochemistry whether these cytokines are spatially correlated with LOX-1 expression in advanced atherosclerotic lesions. We found upregulation of LOX-1 expression in SMC in a dose- and time-dependent manner after incubation with IL-1alpha, IL-1beta, and TNF-alpha. Simultaneous incubation with these cytokines at saturated concentrations had an additive effect on LOX-1 expression. The PPARgamma activator, 15d-PGJ(2), however, inhibited IL-1beta-induced upregulation of LOX-1. In the intima of atherosclerotic lesions regions of IL-1alpha, IL-1beta, and TNF-alpha expression corresponded to regions of LOX-1 expression.

CONCLUSIONS

We suppose that upregulated LOX-1 expression in SMC of advanced atherosclerotic lesions is a response to these proinflammatory cytokines. Moreover, the proinflammatory effects of these cytokines can be decreased by the antiinflammatory effect of PPARgamma.

PPARbeta/delta potentiates PPARgamma-stimulated adipocyte differentiation

It is well established that peroxisome proliferator-activated receptor-gamma (PPARgamma) has a critical role in modulating adipocyte differentiation based on gain-of-function and loss-of-function experiments. However, recent gain-of-function experiments suggest that PPARbeta may also have a role in mediating adipocyte differentiation. Because ligands for PPARs can activate more than one receptor isoform, the specific role of PPARbeta in adipocyte differentiation was examined using PPARbeta-null adipocytes. Wild-type adipocytes accumulate lipids in response to differentiation signaling induced from standard differentiation medium, and this effect is significantly reduced in PPARbeta-null adipocytes. The addition of the PPARbeta ligand L165041 to the standard differentiation medium causes enhanced adipocyte differentiation and lipid accumulation, and this effect is diminished in adipocytes lacking expression of PPARbeta. Treatment of wild-type adipocytes with the PPARgamma ligand troglitazone causes accelerated adipocyte differentiation and lipid accumulation, and this effect is marginally reduced in PPARbeta-null adipocytes. Expression patterns of mRNA markers of early and late adipocyte differentiation are consistent with the morphological and biochemical differences observed. Results from these studies demonstrate that in the absence of PPARbeta expression, adipocyte differentiation is significantly impaired, providing loss-of-function evidence supporting a role for this receptor in adipocyte differentiation. These results also demonstrate that L165041-stimulated adipocyte differentiation and lipid accumulation is mediated by PPARbeta. In addition, as the ability of troglitazone to induce adipocyte differentiation is also impaired in PPARbeta null adipocytes, this suggests that both PPARbeta and PPARgamma isoforms are required to facilitate maximal lipid accumulation and differentiation during adipogenesis.

Influence of peroxisome proliferator-activated receptor activation by its endogenous ligand 15-deoxy 12,14 prostaglandin J2 on nitric oxide production in term placental tissues from diabetic women

Diabetes induces alterations which condition placental remodelling. The levels of nitric oxide (NO) (a modulator of placental invasiveness, differentiation and proliferation) were higher in term placental explants from diabetic patients when compared to controls. Peroxisome proliferator-activated receptor gamma (PPARgamma) activation by its endogenous ligand 15-deoxy Delta(12,14)prostaglandin J(2) (15dPGJ(2)), is a differentiating factor of adipocytes and other cell types, such as trophoblasts. 15dPGJ(2) is also able to down-regulate NO production in different cell types. Our study evaluated the levels of 15dPGJ(2) and PPARgamma and the influence of PPARgamma activation by 15dPGJ(2) on the production of NO, in term placental tissues from control, pre-gestational and gestational diabetic patients. Our results showed that 15dPGJ(2) was present in human term placenta, and that its levels were diminished in gestational (P<0.05) and pre-gestational (P<0.002) diabetic women when compared to controls. Exogenous 15dPGJ(2) addition (2 x 10(-6) mol/l) down-regulated NO production in placenta from control (P<0.001) and pre-gestational diabetic (P<0.01) patients, but failed to do so in gestational diabetic women, whose placental PPARgamma expression was diminished in comparison to controls (P<0.001). As the exogenous activation of PPARgamma prevented NO overproduction in placenta from pre-gestational diabetic women, it may have the potential to improve fetal outcome in this pathology.

Interleukin 11 treatment alters the protein content of Galpha(i2) and adipogenic transcription factors in 3T3-L1 adipocytes

Exposure of fully differentiated 3T3-L1 adipocytes to 5 nM interleukin 11 (IL-11) resulted in an increase (1.9+/-0.5 fold) in the protein content for the heterotrimeric G protein Galpha(i2). This G protein has been suggested to be involved in the control of the insulin responsive glucose transporter (GLUT4) translocation to the plasma membrane. Conversely, IL-11 had no effect on the content of three other G proteins, involved in insulin action. The alteration in Galpha(i2) protein corresponds to and provides a molecular rationale for our previously described IL-11 induced increase in plasma membrane glucose transporter content and increased rate of glucose transport. In addition, treatment with the cytokine altered the protein content of several transcription factors, C/EBPalpha and CHOP-10 decreased while PPARgamma and C/EBPbeta increased. These changes in transcription factor content are consistent with an alteration of phenotype with the cells reverting to an earlier stage of the differentiation process in response to IL-11.

Novel expression of resistin in rat testis: functional role and regulation by nutritional status and hormonal factors

Resistin, a recently cloned adipose-secreted factor, is primarily involved in the modulation of insulin sensitivity and adipocyte differentiation. However, additional metabolic or endocrine functions of this molecule remain largely unexplored. In this study, a series of experiments were undertaken to explore the potential expression, regulation and functional role of this novel adipocytokine in rat testis. Resistin gene expression was demonstrated in rat testis throughout postnatal development, with maximum mRNA levels in adult specimens. At this age, resistin peptide was immunodetected in interstitial Leydig cells and Sertoli cells within seminiferous tubules. Testicular expression of resistin was under hormonal regulation of pituitary gonadotropins and showed stage-specificity, with peak expression values at stages II-VI of the seminiferous epithelial cycle. In addition, testicular resistin mRNA was down-regulated by the selective agonist of PPARγ, rosiglitazone, in vivo and in vitro. Similarly, fasting and central administration of the adipocyte-derived factor, leptin, evoked a significant reduction in testicular resistin mRNA levels, whereas they remained unaltered in a model of diet-induced obesity. From a functional standpoint, resistin, in a dose-dependent manner, significantly increased both basal and choriogonadotropin-stimulated testosterone secretion in vitro. Overall, our present results provide the first evidence for the expression, regulation and functional role of resistin in rat testis. These data underscore a reproductive facet of this recently cloned molecule, which may operate as a novel endocrine integrator linking energy homeostasis and reproduction.

Design, synthesis, and evaluation of a new class of noncyclic 1,3-dicarbonyl compounds as PPARα selective activators

Lipid accumulation in nonadipose tissues is increasingly linked to the development of type 2 diabetes in obese individuals. We report here the design, synthesis, and evaluation of a series of novel PPARalpha selective activators containing 1,3-dicarbonyl moieties. Structure-activity relationship studies led to the identification of PPARalpha selective activators (compounds 10, 14, 17, 18, and 21) with stronger potency and efficacy to activate PPARalpha over PPARgamma and PPARdelta. Experiments in vivo showed that compounds 10, 14, and 17 had blood glucose lowering effect in diabetic db/db mouse model after two weeks oral dosing. The data strongly support further testing of these lead compounds in other relevant disease animal models to evaluate their potential therapeutic benefits.

?-Lipoic acid-based PPAR? agonists for treating inflammatory skin diseases

Novel thiazolidinedione derivatives of the potent antioxidant, alpha-lipoic (thioctic, 1,2-dithiolane) acid, were prepared. The prototype N-(2-[4-[2,4-dioxo(1,3-thiazolidin-5-yl)methyl]phenoxy]ethyl)-5-(1,2-dithiolan-3-yl)- N-methylpentanamide (designated BP-1003), and dithioester derivatives thereof were shown to be potent activators of peroxisome proliferator-activated receptor gamma (PPARgamma) (EC(50) range 15-101 nM) and modest activators of PPARalpha (EC(50) 5 microM). Both the relatively hydrophobic dithiolane prototype, BP-1003, and its water-soluble dithioglycinate derivative, BP-1017, were shown to inhibit the proliferation of human keratinocytes and suppress the production of interleukin-2 by human peripheral lymphocytes to a greater extent than the antidiabetic thiazolidinedione, rosiglitazone. Both oral and topical administration of BP-1017 showed significant antiinflammatory effects in the oxazolone-sensitized mouse model of allergic contact dermatitis (ACD). These findings suggest that water-soluble lipoic acid-based thiazolidinediones may be efficacious as oral and topical agents for treating inflammatory skin conditions such as contact dermatitis, atopic dermatitis, and psoriasis.

A potential role of 15-deoxy-delta(12,14)-prostaglandin J2 for induction of human articular chondrocyte apoptosis in arthritis

The cyclopentenone prostaglandin (PG) J2 is formed within the cyclopentenone ring of the endogenous prostaglandin PG D2 by a nonenzymatic reaction. The PG J family is involved in mediating various biological effects including the regulation of cell cycle progression and inflammatory responses. Here we demonstrate the potential role of 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PG J2) in human articular chondrocyte apoptosis. 15d-PG J2 was released by human articular chondrocytes and found in joint synovial fluids taken from osteoarthritis or rheumatoid arthritis patients. Proinflammatory cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) up-regulated chondrocyte release of 15d-PG J2. PG D2 synthase mRNA expression was up-regulated by IL-1beta, TNF-alpha, or nitric oxide. 15d-PG J2 induced apoptosis of chondrocytes from osteoarthritis or rheumatoid arthritis patients as well as control nonarthritic subjects in a time- and dose-dependent manner and in a peroxisome proliferator-activated receptor gamma-dependent manner. Peroxisome proliferator-activated receptor gamma expression was up-regulated by IL-1beta and TNF-alpha. Inhibition of NF-kappaB, and the activation of p38 MAPK were also found to be involved in 15d-PG J2-induced chondrocyte apoptosis. Such signal pathways led to the activation of the downstream pro-apoptotic molecule p53 and caspase cascades. Together, these results suggest that 15d-PGJ2 may play an important role in the pathogenesis of arthritic joint destruction via a regulation of chondrocyte apoptosis.

Peroxisome proliferator-activated receptor gamma activation can regulate beta-catenin levels via a proteasome-mediated and adenomatous polyposis coli-independent pathway

The transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma) belongs to the family of nuclear hormone receptors and consists of two isotypes, PPARgamma1 and PPARgamma2. Our earlier studies have shown that troglitazone (TZD)-mediated activation of PPARgamma2 in hepatocytes inhibits growth and attenuates cyclin D1 transcription via modulating CREB levels. Because this process of growth inhibition was also associated with an inhibition of beta-catenin expression at a post-translational level, our aim was to elucidate the mechanism involved. beta-Catenin is a multifunctional protein, which can regulate cell-cell adhesion by interacting with E-cadherin and other cellular processes via regulating target gene transcription in association with TCF/LEF transcription factors. Two adenomatous polyposis coli (APC)-dependent proteasomal degradation pathways, one involving glycogen synthase kinase 3beta (GSK3beta) and the other involving p53-Siah-1, degrade excess beta-catenin in normal cells. Our immunofluorescence and Western blot studies indicated a TZD-dependent decrease in cytoplasmic and membrane-bound beta-catenin, indicating no increase in its membrane translocation. This was associated with a reduction in E-cadherin expression. PPARgamma2 activation inhibited GSK3beta kinase activity, and pharmacological inhibition of GSK3beta activity was unable to restore beta-catenin expression following PPARgamma2 activation. Additionally, this beta-catenin degradation pathway was operative in cells, with inactivating mutations of both APC and p53. Inhibition of the proteasomal pathway inhibited PPARgamma2-mediated degradation of beta-catenin, and incubation with TZD increased ubiquitination of beta-catenin. We conclude that PPARgamma2-mediated suppression of beta-catenin levels involves a novel APC/GSK3beta/p53-independent ubiquitination-mediated proteasomal degradation pathway.

Be Fit or Be Sick: Peroxisome Proliferator-Activated Receptors Are Down the Road

Investigating metabolism by unveiling the functions of the nuclear receptors peroxisome proliferator-activated receptors (PPARs) in the numerous intricate pathways ensuring energy homeostasis and fitness has been extremely rewarding. Major lines of research were initially determined by the first-characterized crucial roles of PPARalpha in fatty oxidation and of PPARgamma in adipocyte differentiation and lipid storage. Today, the molecular bases of the functional links between glucose, lipid, and protein metabolism, under the important but nonexclusive control of PPARalpha and PPARgamma, are starting to be uncovered. In addition, in the last couple of years evidence has been provided for an important role of PPARbeta (delta) in lipid metabolism. Inevitably, such actors of metabolic homeostasis are implicated in the physiopathology of complex metabolic disorders, such as those constituting the metabolic syndrome, resulting in atherosclerosis and cardiovascular diseases. This review presents a summary of the recent findings on their dual involvement in health and disease.

Pharmacological characteristics of a novel nonthiazolidinedione insulin sensitizer, FK614

We evaluated antidiabetic effects of 3-(2,4-dichlorobenzyl)-2-methyl-N-(pentylsulfonyl)-3 H-benzimidazole-5-carboxamide (FK614), a benzimidazole derivative without a thiazolidinedione structure, which was obtained using C57BL/KsJ-db/db mice (db/db mice). In db/db mice, the potency of FK614 for hypoglycemic effect was comparable to that of rosiglitazone and approximately 15-fold greater than that of pioglitazone. FK614 also showed a potent attenuating effect on hypertriglyceridemia in db/db mice, as well as rosiglitazone and pioglitazone. In C57BL/6J-ob/ob mice (ob/ob mice), ED(50) values of FK614 and pioglitazone for hypoinsulinemic effect were 1.3 and 11.8 mg/kg, respectively. FK614 also improved the impaired glucose tolerance in ob/ob mice. In normal rats, FK614 did not influence plasma glucose and insulin levels but significantly decreased both plasma triglyceride and nonesterified fatty acid levels. FK614 was found to activate peroxisome proliferator-activated receptor (PPAR)gamma-mediated transcriptional activity in the reporter gene assay as well as thiazolidinedione derivatives, although its maximum effect was less than that of thiazolidinedione derivatives. In rat toxicity studies, hemodilution effects for FK614 were less than that for rosiglitazone. Overall, these studies suggest that FK614 improves insulin resistance in such animal models through activation of PPARgamma-mediated transcriptional activity and that it would be a new therapeutic candidate with potential for the treatment of type 2 diabetic patients.

Effects of salidroside on carbohydrate metabolism and differentiation of 3T3-L1 adipocytes

OBJECTIVE

To observe the effects of salidroside on carbohydrate metabolism and differentiation of 3T3-L1 adipocytes.

METHODS

3H-glucose uptaking rate in adipocytes treated by salidroside was detected. Adipocytes treated by salidroside in differentiation were stained by oil red O and analyzed by spectrophotography quantitatively. The expression of PPAR-gamma and C/EBP-alpha mRNA relating to differentiation of adipocytes was detected by reverse transcription PCR.

RESULTS

3H-glucose uptaking rate in the salidroside group was 110.4%, higher than that in the blank control group (P < 0.01). Salidroside suppressed the differentiation of 3T3-L1 pre-adipocytes and down-regulated the expression of PPAR-gamma and C/EBP-alpha mRNA (P < 0.01, vs control group).

CONCLUSION

Salidroside promotes the 3H-glucose uptaking, suppresses the differentiation and down-regulates the expression of PPAR-gamma and C/EBP-alpha mRNA in 3T3-L1 adipocytes.

Antidiabetic and hypolipidemic potential of DRF 2519—a dual activator of PPAR-α and PPAR-γ

We investigated the biological activity of Dr. Reddy's Research Foundation (DRF) 2519, a benzoxazinone analogue of the thiazolidinedione class of compounds. In the in vitro transactivation assay, DRF 2519 showed interesting dual activation of Peroxisome Proliferator Activated Receptor (PPAR) alpha and gamma. In insulin-resistant ob/ob mouse model, DRF 2519 showed significant alleviation of insulin resistance and dyslipidemia, which is better than rosiglitazone. Fatty Zucker rats treated with DRF 2519 showed better reduction of plasma insulin, triglyceride and free fatty acid levels than those treated with rosiglitazone. In addition, these rats were able to clear plasma lipids better when challenged with exogenous lipid (i.v.). DRF 2519 treatment resulted in improved plasma lipid profiles in high-fat-fed Sprague-Dawley rats. Treated rats showed better plasma lipid clearance and hepatic triglyceride secretion. When compared to DRF 2519, fenofibrate was comparatively less efficacious while rosigltiazone showed no activity in these models. In ex vivo studies, DRF 2519 showed induction of liver acyl CoA oxidase mRNA and increase in lipoprotein lipase (LPL) protein expression and activity in adipose tissue. In the in vitro studies, DRF 2519 inhibited the lipid biosynthesis and secretion of apolipoprotein B from human hepatoma (Hep)G2 cells. It also enhanced insulin-induced relaxation of rat aortic smooth muscle. These results indicate that DRF 2519, a dual activator of PPAR-alpha and gamma, could be an interesting development candidate in the management of metabolic disorders and associated complications.

Baseline and CRH-stimulated ACTH and cortisol levels after administration of the peroxisome proliferator-activated receptor-gamma ligand, rosiglitazone, in Cushing's disease

The ability of acute rosiglitazone administration in influencing ACTH/cortisol secretion in basal conditions and after CRH stimulation was studied in patients with Cushing's disease. Ten patients (8 women and 2 men, aged 18-65 yr) with Cushing's disease were enrolled in the study: 6 of them had previously undergone unsuccessful surgery and 4 were untreated. Plasma ACTH and serum cortisol levels were evaluated at serial time points for 3 h during saline infusion and after the administration of rosiglitazone (8 mg, po) and for 1 h after the injection of CRH (1 microg/kg iv) given alone or 30 min following rosiglitazone administration. The 4 tests were performed in all subjects in randomized order on different days. No significant difference was observed between the pattern of hormone secretion during saline alone and after rosiglitazone, as evaluated by two-way analysis of variance (ANOVA). The integrated areas under the curves (AUCs) were also not significantly different (ACTH: 5683 +/- 1038 vs 6111 +/- 1007 pg/ml/180 min; cortisol: 2333 +/- 267 vs 2902 +/- 486 microg/dl/180 min). In addition, there was no difference for ACTH and cortisol responses to CRH given either alone or after rosiglitazone, when evaluated as peak, increment or AUC; the pattern of the responses analyzed by two-way ANOVA was also similar.

IN CONCLUSION

1) the administration of a single dose of rosiglitazone did not decrease ACTH/cortisol levels or blunt their response after CRH injection; 2) the activation of PPAR-gamma receptors by rosiglitazone seems unable to affect ACTH and cortisol secretion, at least in acute conditions, in patients with ACTH-secreting pituitary adenomas.

Eicosapentaenoic acid and gamma-linolenic acid increase hippocampal concentrations of IL-4 and IL-10 and abrogate lipopolysaccharide-induced inhibition of long-term potentiation

Inflammatory changes in brain exert a negative impact on cognitive function and in animal studies, these changes are associated with impairment in hippocampal-dependent learning paradigms and in long-term potentiation (LTP), which is a putative biological substrate for learning and/or memory. Lipopolysaccharide (LPS), a component of the cell wall of gram negative bacteria, induces inflammatory changes in the brain and leads to impairment of LTP. Since eicosapentaenoic acid (EPA) inhibits LPS-induced changes in vitro, we assessed the possibility that treatment of rats with EPA, alone or in combination with gamma-linolenic acid (GLA) might inhibit LPS-induced changes in vivo. The data presented indicate that the LPS-induced inhibition of LTP and decrease in hippocampal concentration of anti-inflammatory cytokines IL-10 and IL-4 are blocked in rats treated with EPA, GLA or both. The evidence suggests that these effects may be coupled with fatty acid-induced up-regulation of peroxisome proliferator-activated receptor-gamma which possesses known anti-inflammatory effects.

Role of PPARgamma and EGFR signalling in the urothelial terminal differentiation programme

Recently, considerable interest has focused on the ability of activated peroxisome proliferator-activated receptor gamma (PPARgamma) to promote cytodifferentiation in adipocytes and some carcinoma cells; however, the role of PPARgamma in normal epithelial cytodifferentiation is unknown. Using uroplakin (UP) gene expression as a specific correlate of terminal urothelial cytodifferentiation, we investigated the differentiation-inducing effects of PPARgamma activation in normal human urothelial (NHU) cells grown as finite cell lines in monoculture. Two high-affinity activators of PPARgamma, troglitazone (TZ) and rosiglitazone (RZ) induced the expression of mRNA for UPII and UPIb and, to a lesser extent, UPIa. The specificity of the effect was shown by pretreating cells with a PPARgamma antagonist, GW9662, which attenuated the TZ-induced response in a dose-specific manner. The PPARgamma-mediated effect on UP gene expression was maximal when there was concurrent inhibition of autocrine-activated epidermal growth factor receptor (EGFR) signalling through either the phosphatidylinositol 3-kinase or extracellular signal-regulated kinase (ERK) pathways. The use of a specific EGFR tyrosine kinase inhibitor, PD153035, correlated with PPARgamma dephosphorylation and translocation to the nucleus, indicating a mechanism for regulating the balance between proliferation and differentiation. This is the first identification of specific factors involved in regulating differentiation-associated gene changes in urothelium and the first unambiguous evidence of a role for PPARgamma signalling in the terminal differentiation programme of a normal epithelium.