Interaction of ligands for the peroxisome proliferator-activated receptor gamma with the endocannabinoid system

BACKGROUND AND PURPOSE: There is good evidence that agents interacting with the endocannabinoid system in the body can also interact with the peroxisome proliferator-activated receptor gamma. The present study was designed to test whether the reverse is true, namely whether peroxisome proliferator-activated receptor gamma ligands have direct effects upon the activity of the endocannabinoid metabolizing enzyme fatty acid amide hydrolase. EXPERIMENTAL APPROACH: Fatty acid amide hydrolase activity was measured in rat brain homogenates, C6 glioma and RBL2H3 basophilic leukaemia cells. Cellular uptake of anandamide was also assessed in these cells. KEY RESULTS: Peroxisome proliferator-activated receptor gamma activators inhibited the metabolism of the endocannabinoid anandamide in rat brain homogenates with an order of potency MCC-555 > indomethacin approximately ciglitazone approximately 15-deoxy-Delta(12,14)-prostaglandin J(2) approximately pioglitazone > rosiglitazone > troglitazone. The antagonists BADGE, GW9662 and T0070907 were poor inhibitors of anandamide hydrolysis. The inhibition by ciglitazone was competitive and increased as the pH of the assay buffer was decreased; the K(i) value at pH 6.0 was 17 microM. In intact C6 glioma cells assayed at pH 6.2, significant inhibition of anandamide hydrolysis was seen at 3 microM ciglitazone, whereas 100 microM was required to produce significant inhibition at pH 7.4. Ciglitazone also interacted with monoacylglycerol lipase as well as with cannabinoid CB(1) and CB(2) receptors. CONCLUSIONS AND IMPLICATIONS: Ciglitazone may be useful as a template for the design of novel dual action anti-inflammatory agents which are both inhibitors of fatty acid amide hydrolase and agonists at the peroxisome proliferator-activated receptor gamma.     

Inhibition of in vivo glioma growth and invasion by peroxisome proliferator-activated receptor gamma agonist treatment

The peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear hormone receptor family, represents a possible new target in glioma therapy. Because PPARgamma plays a crucial role in regulation of insulin sensitivity, synthetic agonists are already in clinical use for type II diabetes treatment. Beyond these metabolic effects, PPARgamma agonists exhibit antineoplastic effects. In this study, we investigated the antineoplastic effects of the PPARgamma agonist pioglitazone in glioma cells. Pioglitazone reduced cellular viability of rat, human, and PPARgamma-overexpressing glioma cells in vitro in a time- and concentration-dependent manner. No antineoplastic effects were induced by pioglitazone in glioma cells overexpressing a PPARgamma mutant. Furthermore, proliferation was reduced by pioglitazone, as measured by Ki-67 immunoreactivity, in vitro. Continuous intracerebral infusion of pioglitazone into gliomas induced by intrastriatal injection of C6 cells reduced tumor volumes by 83%. Oral administration of pioglitazone reduced tumor volumes by 76.9%. Subsequent brain tissue analysis revealed induction of apoptotic cell death. Ki-67 expression and BrdU incorporation revealed a reduction of proliferation in vivo. Reduced invasion of C6 cells and lower matrix metalloproteinase 9 levels in vivo indicate pioglitazone-mediated reduction of invasion. Together, these data indicate that pioglitazone may be of potential use in treatment of malignant gliomas.     

Ligand-induced stabilization and activation of peroxisome proliferator-activated receptor gamma

Peroxisome proliferator-activated receptor gamma belongs to the nuclear receptor superfamily and is activated by the antidiabetic drugs rosiglitazone and pioglitazone. Ligand-independent constitutive activity of peroxisome proliferator-activated receptor gamma is also demonstrated. X-ray crystallographic structures show that the active or inactive conformations of the receptor are determined by the position of helix 12 in the C-terminal end. In this study, molecular dynamics simulations were used to gain molecular insight into the activation process and the structural stability of inactive and active peroxisome proliferator-activated receptor gamma receptor structure. The simulations showed: (i) during molecular dynamics simulations without agonist at the active site, the receptor structure with helix 12 in a position corresponding to activated receptor structure was structurally more stable than with helix 12 in a position corresponding to inactive receptor structure, which may contribute to the constitutive activity of the receptor; (ii) docosahexenoic acid stabilized the active receptor conformation more efficiently than the glitazones; (iii) docosahexenoic acid, but not glitazones, induced structural changes into the inactive receptor structure such that helix 12 was shifted into a position more similar to that of an active receptor structure, which indicate that docosahexenoic acid is a more effective peroxisome proliferator-activated receptor gamma agonist than the glitazones.     

The potential of peroxisome proliferator-activated receptor gamma (PPARgamma) ligands in the treatment of hematological malignancies

PPARgamma has emerged as a key regulator of cell growth and survival, whose activity is modulated by a number of synthetic and natural ligands. Here we shall review the activities of PPARgamma ligands in the control of immune cell proliferation, differentiation and apoptosis and their potential therapeutic applications to hematological malignancies.     

Synthetic peroxisome proliferator-activated receptor gamma agonists rosiglitazone and troglitazone suppress transcription by promoter 3 of the human thromboxane A2 receptor gene in human erythroleukemia cells

The human thromboxane (TX)A2 receptor (TP) gene encodes two TP isoforms, TPalpha and TPbeta, that are regulated by distinct promoters designated promoter Prm1 and Prm3, respectively. Previous studies established that 15d-Delta12,14-prostaglandin J2 (15d-PGJ2) selectively inhibits Prm3 activity and TPbeta expression through a peroxisome proliferator-activated receptor (PPAR)gamma mechanism without affecting Prm1 activity or TPalpha expression in human megakaryocytic erythroleukemia (HEL) 92.1.7 cells. Herein, we investigated the effect of synthetic thiazolidinedione (TZD) PPARgamma ligands rosiglitazone and troglitazone on TP gene expression in HEL cells. Like 15d-PGJ2, both TZDs suppressed Prm3 activity, TPbeta mRNA expression and TP-mediated calcium mobilization without affecting Prm1 or TPalpha mRNA expression. However, unlike 15d-PGJ2, both TZDs mediated their PPARgamma-dependent effects through trans-repression of an activator protein-1 (AP-1) element, a site previously found to be critical for basal Prm3 activity. These data provide further evidence for the role of PPARgamma in regulating the human TP gene; they highlight further differences in TPalpha and TPbeta expression/regulation and point to essential differences between natural and synthetic PPARgamma agonists in mediating those effects.     

Ligands of peroxisome proliferator-activated receptor gamma induce apoptosis in multiple myeloma

The activation of proliferator-activated receptor gamma (PPAR-gamma) by its natural and synthetic ligands induces apoptosis in several tumor cell lines, including malignant B-lineage cells. We investigated whether treatment with pioglitazone (PGZ), rosiglitazone (RGZ) or 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) inhibited tumor cell growth in five human multiple myeloma cell lines (LP-1, U-266, RPMI-8226-S, OPM-2 and IM-9) and human bone marrow myeloma cells expressing PPAR-gamma protein. MTT assays revealed growth arrest induced by the natural activator of PPAR-gamma 15d-PGJ2 and a lower antiproliferative effect with thiazolidinediones (PGZ and RGZ) in a dose-dependent manner. Induction of apoptosis was indicated by Annexin-V staining. At a dose of 50 microM, 15d-PGJ2 led to a high rate of apoptosis in all cell lines (60-92%). Furthermore, induction of apoptosis in sorted bone marrow plasma cells from myeloma patients was detected. Thiazolidinediones comprise anti-myeloma activity in vitro and should be explored further for the treatment of multiple myeloma.     

Arsenic inhibits the adipogenic differentiation of mesenchymal stem cells by down-regulating peroxisome proliferator-activated receptor gamma and CCAAT enhancer-binding proteins

Arsenic remains a top environmental concern in the United States as well as worldwide because of its global existence and serious health impacts. Apoptotic effect of arsenic in human mesenchymal stem cells (hMSCs) has been identified in our previous study; the effects of arsenic on hMSCs remain largely unknown. Here, we report that arsenic inhibits the adipogenic differentiation of human mesenchymal stem cells (hMSCs). Arsenic reduced the formation of lipid droplets and the expression of adipogenesis-related proteins, such as CCAAT enhancer binding protein-(C/EBPs), peroxisome proliferator-activated receptor-gamma (PPAR-γ), and adipocyte fatty acid–binding protein aP2 (aP2). Arsenic mediates this process by sustaining PPAR-γ activity. In addition, inhibition of PPAR-γ activity with T0070907 and up-regulation with its agonist troglitazone, showed the direct association of PPAR-γ and arsenic-mediated inhibition of differentiating hMSCs. Taken together, these results indicate that arsenic inhibits adipogenic differentiation through PPAR-γ pathway and suggest a novel inhibitory effect of arsenic on adipogenic differentiation in hMSCs.     

Anti-proliferative effect of peroxisome proliferator-activated receptor gamma agonists on human malignant melanoma cells in vitro

Malignant melanoma has a poor reputation for early spread and no curative treatment is yet available. As peroxisome proliferator-activated receptor gamma (PPARgamma) agonists (glitazones) have recently been shown to have growth-inhibiting effects on different cancer lineages, the aim of this study was to analyze the effects of four glitazones (rosiglitazone, ciglitazone, pioglitazone and troglitazone) on the growth of six human malignant melanoma cells in vitro. Proliferation of six human melanoma cell lines under glitazone treatment over a broad concentration range (0.15-300 micromol/l) was assessed by means of the XTT cell proliferation assay, and expression of PPARgamma in these cell lines was analyzed using both immunohistochemical and molecular biological techniques. All four glitazones showed a significant dose-dependent anti-proliferative effect on all six cell lines starting at a concentration of 0.3 micromol/l, with ciglitazone being the most potent inhibitor of cell growth, followed by troglitazone, rosiglitazone and pioglitazone. PPARgamma was predominantly localized in the cytoplasm; however, there were quantitative differences in PPARgamma expression between the different cell lines as demonstrated by quantification of Western blots. As an already approved class of drugs, glitazones have been found to significantly inhibit growth of human malignant melanoma cells in vitro and might be a promising tool for further therapeutic studies.     

2-hydroxy-4'-methoxychalcone inhibits proliferation and inflammation of human aortic smooth muscle cells by increasing the expression of peroxisome proliferator-activated receptor gamma

Chalcone is a class of flavonoid compounds that are widely biosynthesized in plants. Epidemiological studies suggest that increased intake of flavonoids from fruits and vegetables reduces the risk of cardiovascular disease. However, the effect of chalcone on cardiovascular diseases has not been fully investigated. The aims of this study were to evaluate the antiatherosclerotic effect of 2-hydroxy-4'-methoxychalcone (AN07, a synthetic chalcone derivate) and to investigate its potential pharmacological mechanisms. Oxidized low-density lipoprotein (Ox-LDL) has been reported to stimulate proliferation of human aortic smooth muscle cells and that is one of the mechanisms resulting in atherosclerosis. In this study, we demonstrate that AN07 significantly inhibits the Ox-LDL-induced proliferation of human aortic smooth muscle cells. This effect is mediated via the inhibition of p44/42 mitogen-activated protein kinase and E-twenty six 1 phosphorylations. In the effect of anti-inflammation, AN07 decreases the Ox-LDL-stimulated upregulation of interleukin (IL) 1β and IL-6. In addition, AN07 acts synergistically with rosiglitazone and pioglitazone to inhibit the Ox-LDL-induced proliferation of human aortic smooth muscle cells and upregulation of cyclin D1, cyclin D3, IL-1β, and IL-6. These effects are a result of an increase in peroxisome proliferator-activated receptor gamma mRNA and protein expression stimulated by AN07 in human aortic smooth muscle cells. In conclusion, the chalcone derivate AN07 has versatile therapeutic potential against atherosclerosis by acting as peroxisome proliferator-activated receptor gamma inducer, p44/42 mitogen-activated protein kinase inhibitor, and cell cycle blocker.     

Novel peroxisome proliferator-activated receptor ligands for Type 2 diabetes and the metabolic syndrome

As the incidence of Type 2 diabetes has reached near epidemic proportions, the quest for novel therapies to combat this disorder has intensified dramatically. In recent years, the peroxisome proliferator-activated receptor (PPAR) family has received tremendous attention as perhaps an ideal target class to address the multiple metabolic anomalies associated with the diabetic state. This review focuses on a variety of novel PPAR approaches currently being investigated for Type 2 diabetes or the metabolic syndrome, including the highly potent selective PPAR agonists, PPAR combination agonists and alternative PPAR ligands.     

Novel peroxisome proliferator-activated receptor ligands for Type 2 diabetes and the metabolic syndrome

As the incidence of Type 2 diabetes has reached near epidemic proportions, the quest for novel therapies to combat this disorder has intensified dramatically. In recent years, the peroxisome proliferator-activated receptor (PPAR) family has received tremendous attention as perhaps an ideal target class to address the multiple metabolic anomalies associated with the diabetic state. This review focuses on a variety of novel PPAR approaches currently being investigated for Type 2 diabetes or the metabolic syndrome, including the highly potent selective PPAR agonists, PPAR combination agonists and alternative PPAR ligands.     

过氧化物酶体增生物激活受体γ激动剂致水肿机制及预防的研究进展

过氧化物酶体增生物激活受体γ（peroxisome proliferator-activated receptor gamma,PPAR-γ）激动剂主要包括噻唑烷二酮类（thiazolidinediones,TZDs）和非噻唑烷二酮类新型PPAR-γ激动剂。噻唑烷二酮类药物常用的有曲格列酮、吡咯列酮及罗格列酮。PPAR-γ激动剂的常见不良反应之一为水肿,并可加重或引致充血性心力衰竭。水肿发生率为3%～28.9%;PPAR-γ激动剂和其他口服降血糖药或胰岛素合用可增加水肿发生率。PPAR-γ引起水肿的机制涉及水钠潴留、血管扩张以及血管通透性增加等因素,特别是分布于远端肾小管和集合管的水、钠转运蛋白调节异常对水钠潴留的发生起重要作用。PPAR-γ激动剂引起的水肿一般较轻,停药后可消退。糖尿病合并中、重度充血性心力衰竭患者[NYHA（New York Heart Association）Ⅲ或Ⅳ级]避免用PPAR-γ激动剂,合并轻度充血性心力衰竭患者（NYHAI至Ⅱ级）应慎用,尽可能用最小剂量,必需时,剂量应逐渐增加,可联合应用利尿剂,并应严密监测患者体重和水肿的发生情况。预防治疗水肿的方法包括应用新的选择性PPAR-γ调节剂、蛋白激酶C-β或上皮细胞钠通道的特异性抑制剂及PPAR-γ拮抗剂。     

Curcumin inhibits trinitrobenzene sulphonic acid-induced colitis in rats by activation of peroxisome proliferator-activated receptor gamma

Curcumin is a widely used spice with anti-inflammatory and anti-cancer properties. It has been reported that curcumin held therapeutic effects on experimental colitis by inhibition of nuclear factor kappa B (NF-kappaB). The peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor with anti-tumor and anti-inflammatory effects and its activation may inhibit the nuclear translocation of NF-kappaB. Several studies have shown that PPARgamma ligands had an important therapeutic effect in colitis. However there is no report about the alteration of PPARgamma in trinitrobenzene sulphonic acid (TNBS)-induced colitis treated with curcumin. In this study, we administered curcumin (30 mg/kg/day) by intraperitoneal injection immediately after colitis was induced and the injection lasted for two weeks. have evaluated the effects of curcumin on the colitis induced by trinitrobenzene sulphonic acid (TNBS). Curcumin (30 mg/kg d) was administered by intraperitoneal just after colitis was induced and lasted for two weeks. Therapeutic effects of dexamethasone (Dex, 2 mg/kg d) alone and the combined effects of curcumin+Dex were also examined. We found that curcumin improved long-term survival rate of disease-bearing rats, promoted rat body weight recovery, and decreased macroscopic scores of the colitis. The expression levels of PPARgamma, 15-deoxy-D12,14-prostaglandin J(2) (15d-PGJ(2)) and prostaglandin E(2) (PGE(2)) were all increased, but the expression level of cyclooxygenase-2 (COX-2) was decreased in rats after administration of curcumin. Treatment with Dex improved PPARgamma expression and inhibited the expression of COX-2, 15d-PGJ(2) and PGE(2). Combined effects of curcumin+Dex were similar to that of Dex. In summary, curcumin showed therapeutic effects on TNBS-induced colitis and the mechanisms by which curcumin exerts its effects may involve activation of PPARgamma and its ligands.