leptin and ciglitazone

The obesity hormone leptin has been implicated in breast cancer development. Breast cancer cells express the leptin receptor and are able to synthesize leptin in response to obesity-related stimuli. Furthermore, leptin is a positive regulator of vascular endothelial growth factor (VEGF) and high levels of both proteins are associated with worse prognosis in breast cancer patients. Peroxisome proliferator-activated receptor γ (PPARγ) ligands are therapeutic agents used in patient with Type 2 diabetes and obesity which have recently been studied for their potential anti-tumor effect. Here, we studied if these compounds, ciglitazone and GW1929, can affect the expression of leptin and VEGF in breast cancer cells. In MDA-MB-231 and MCF-7 breast cancer cells, treatment with submolar concentrations of ciglitazone and GW1929 elevated the expression of leptin and VEGF mRNA and protein, and increased cell viability and migration. These effects coincided with increased recruitment of PPARγ to the proximal leptin promoter and decreased association of a transcriptional factor Sp1 with this DNA region.

Topics: Benzophenones; Binding Sites; Breast Neoplasms; Cell Movement; Cell Survival; Dose-Response Relationship, Drug; Female; Gene Expression Regulation, Neoplastic; Humans; Leptin; Ligands; MCF-7 Cells; PPAR gamma; Promoter Regions, Genetic; RNA, Messenger; Sp1 Transcription Factor; Thiazolidinediones; Tyrosine; Vascular Endothelial Growth Factor A

Leptin is a peptide known to play a profibrogenic role in hepatic stellate cells (HSCs). Peroxisome-proliferator activated receptor (PPAR)-gamma ligands are suggested to have an anti-fibrogenic effect on HSCs. Since the association of these two factors in HSC activation has not been demonstrated, we hypothesized that PPAR-gamma ligands would suppress leptin-induced HSC activation and regulate leptin receptor expression. Immortalized human HSCs were activated by either leptin or platelet-derived growth factor (PDGF) in one group. In another group, ciglitazone, a PPAR-gamma ligand, was treated before the leptin or PDGF stimulation. Proliferation of human HSCs was achieved by both PDGF and leptin, and this could be suppressed by ciglitazone. PPAR-gamma mRNA expression was diminished in activated HSCs either by PDGF or leptin, and this was reversed by ciglitazone in both cases. Leptin receptor (OB-R) mRNA expression increased in activated HSCs either by PDGF or leptin, and the expression was inhibited by ciglitazone. Another adipogenic transcription factor, sterol regulatory element-binding protein-1c (SREBP-1c) mRNA expression was decreased either by PDGF or leptin. However, this effect was not reversed by ciglitazone pre-treatment. The inhibitory effect of ciglitazone on leptin-induced HSC proliferation was associated with the reversion of extracellular factor-regulated kinases (ERKs) activation. HSCs were OB-R expressing cells, and ciglitazone could regulate the expression of OB-R mRNA.

Topics: Actins; Blotting, Western; Cell Differentiation; Cell Proliferation; Cells, Cultured; Extracellular Signal-Regulated MAP Kinases; Gene Expression Regulation; Humans; Hypoglycemic Agents; Leptin; Ligands; Liver; Models, Biological; Phosphorylation; Platelet-Derived Growth Factor; PPAR gamma; Receptors, Cell Surface; Receptors, Leptin; RNA, Messenger; Sterol Regulatory Element Binding Protein 1; Thiazolidinediones

Migration of endothelial cells (EC) is a key event in angiogenesis that contributes to neovascularization in diabetic vasculopathy. Leptin induces angiogenesis and is elevated in obesity and hyperinsulinemia. The antidiabetic thiazolidinediones (TZD) inhibit leptin gene expression and vascular smooth muscle cell migration through activation of the peroxisome proliferator-activated receptor-gamma (PPARgamma). This study investigates the role of leptin in EC migration, the chemotactic signaling pathways involved, and the effects of the TZD-PPARgamma ligands troglitazone (TRO) and ciglitazone (CIG) on EC migration. We demonstrate that leptin induces EC migration. Because activation of two signaling pathways, the phosphatidylinositol-3 kinase (PI3K)-->Akt-->eNOS and the ERK1/2 MAPK pathway, is known to be involved in cell migration, we used the pharmacological inhibitors wortmannin and PD98059 to determine if chemotactic signaling by leptin involves Akt or ERK1/2, respectively. Both wortmannin and PD98059 significantly inhibited leptin-induced migration. Treatment with the TZD-PPARgamma-ligands TRO and CIG significantly inhibited the chemotactic response toward leptin. Both PPARgamma-ligands inhibited leptin-stimulated Akt and eNOS phosphorylation, but neither attenuated ERK 1/2 activation in response to leptin. The inhibition of Akt-phosphorylation was accompanied by a PPARgamma-ligand-mediated upregulation of PTEN, a phosphatase that functions as a negative regulator of PI3K-->Akt signaling. These experiments provide the first evidence that activation of Akt and ERK 1/2 are crucial events in leptin-mediated signal transduction leading to EC migration. Moreover, inhibition of leptin-directed migration by the PPARgamma-ligands TRO and CIG through inhibition of Akt underscores their potential in the prevention of diabetes-associated complications.

Topics: Androstadienes; Cell Line; Cell Movement; Chemotaxis; Chromans; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Activation; Enzyme Inhibitors; Flavonoids; Humans; Leptin; Ligands; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Phosphoric Monoester Hydrolases; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; PTEN Phosphohydrolase; Receptors, Cytoplasmic and Nuclear; Signal Transduction; Thiazoles; Thiazolidinediones; Transcription Factors; Troglitazone; Tumor Suppressor Proteins; Wortmannin

The trans10,cis12 (t10c12) isomer of conjugated linoleic acid (CLA) has been shown to inhibit heparin-releasable lipoprotein lipase activity, reduce lipid stores in cultured 3T3-L1 adipocytes, and, when fed to mice, reduce body fat gain. We now report that t10c12 CLA significantly reduced leptin secretion from cultured 3T3-L1 adipocytes, and reduced leptin mRNA levels within the cells. Similar effects were produced by conjugated nonadecadienoic acid (a 19-carbon CLA cognate that is more effective than CLA in reducing body fat gain in mice), the lipoxygenase inhibitor nordihydroguaiaretic acid (which is synergistic with CLA in reducing body fat gain in mice), and ciglitazone (TZD, a PPARgamma agonist). Feeding mice diet supplemented with 0.5% t10c12 CLA for 4 weeks significantly reduced body fat gain, serum leptin levels and adipocyte leptin mRNA expression, without affecting feed intake or body weight. These data provide new insights into apparent mechanistic similarities among t10c12 CLA, CNA, NDGA, and TZD.

Topics: 3T3 Cells; Adipocytes; Animals; Antioxidants; Hypoglycemic Agents; Leptin; Linoleic Acid; Male; Masoprocol; Mice; Mice, Inbred ICR; Thiazoles; Thiazolidinediones

Uncoupling protein-2 (UCP2) is a novel mitochondrial protein that may be involved in the control of energy expenditure. We have previously reported an upregulation of adipose tissue UCP2 mRNA expression during fasting in humans. Analysis of changes in metabolic parameters suggested that fatty acids may be associated with the increased UCP2 mRNA level. Culture of human adipose tissue explants was used to study in vitro regulation of adipocyte UCP2 gene expression. A 48-h treatment with BRL49653 and bromopalmitate, two potent activators of PPARgamma, resulted in a dose-dependent increase in UCP2 mRNA levels. The induction by BRL49653 was rapid (from 6 h) and maintained up to 5 days. TNFalpha provoked a 2-fold decrease in UCP2 mRNA levels. Human recombinant leptin did not affect UCP2 mRNA expression. The data support the hypothesis that fatty acids are involved in the control of adipocyte UCP2 mRNA expression in humans.

Topics: Adipocytes; Adipose Tissue; Adult; Cells, Cultured; Culture Techniques; Dose-Response Relationship, Drug; Female; Gene Expression Regulation; Humans; Ion Channels; Leptin; Membrane Transport Proteins; Middle Aged; Mitochondrial Proteins; Palmitates; Proteins; Receptors, Cytoplasmic and Nuclear; RNA, Messenger; Rosiglitazone; Thiazoles; Thiazolidinediones; Time Factors; Transcription Factors; Transcriptional Activation; Tumor Necrosis Factor-alpha; Uncoupling Protein 2