gw-7647 and ciglitazone

Peroxisome proliferator-activated receptor (PPAR) transcription factors are pharmaceutical drug targets for treating diabetes, atherosclerosis, and inflammatory degenerative diseases. The possible mechanism of interaction between the three PPAR isotypes (alpha, beta/delta, and gamma) is not yet clear. However, this is important both for understanding transcription factor regulation and for the development of new drugs. The present study was designed to compare the effects of combinations of synthetic agonists of PPARalpha [2-[4-[2-[4-cyclohexylbutyl (cyclohexylcarbamoyl)amino]ethyl]phenyl] sulfanyl-2-methylpropanoic acid (GW7647)], PPARbeta/delta [4-(3-(2-propyl-3-hydroxy-4-acetyl)phenoxy)propyloxyphenoxy acetic acid, (L-165041)], and PPARgamma (rosiglitazone, ciglitazone) on inflammatory gene regulation in rat primary astrocytes. We measured cyclooxygenase-2 (COX-2) expression and prostaglandin E(2) synthesis in lipopolysaccharide (LPS)-stimulated cells. PPARalpha, PPARbeta/delta, and PPARgamma knockdown models served to delineate the contribution of each PPAR isotype. Thiazolidinediones enhanced the LPS-induced COX-2 expression via PPARgamma-dependent pathway, whereas L-165041 and GW7647 had no influence. However, the addition of L-165041 potentiated the effect of PPARgamma activation through PPARbeta/delta-dependent mechanism. On the contrary, PPARalpha activation (GW7647) suppressed the effect of the combined L-165041/rosiglitazone application. The mechanism of the interplay arising from combined applications of PPAR agonists involves changes in PPAR expression levels. A PPARbeta/delta overexpression model confirmed that PPARbeta/delta expression level is the point at which PPARgamma and PPARalpha pathways converge in control of COX-2 gene expression. Thus, we discovered that in primary astrocytes, PPARgamma has a positive influence and PPARalpha has a negative influence on PPARbeta/delta expression and activity. A positive/negative-feedback loop is formed by PPARbeta/delta-dependent increase in PPARalpha expression level. These findings elucidate a novel principle of regulation in the signaling by synthetic PPAR agonists that involves modulating the interaction between PPARalpha,-beta/delta, and -gamma isoforms on the level of their expression.

Topics: Animals; Animals, Newborn; Astrocytes; Biomarkers; Brain; Butyrates; Cells, Cultured; Cyclooxygenase 2; Drug Combinations; Gene Expression Regulation, Enzymologic; Glial Fibrillary Acidic Protein; Lipopolysaccharides; Peroxisome Proliferator-Activated Receptors; Phenoxyacetates; Phenylurea Compounds; PPAR alpha; PPAR delta; PPAR gamma; PPAR-beta; Protein Isoforms; Rats; Rosiglitazone; Thiazolidinediones; Time Factors

The phthalates di(2-ethylhexyl)phthalate (DEHP) and di-n-butyl phthalate (DBP) are environmental contaminants with significant human exposures. Both compounds are known reproductive toxins in rodents and DEHP also induces rodent hepatocarcinogenesis in a process believed to be mediated via the peroxisome proliferator-activated receptor alpha (PPARalpha). DEHP and DBP are metabolised to their respective monoesters, mono-(2-ethylhexyl)phthalate (MEHP) and mono-n-butyl phthalate (MBP), which are the active metabolites. MEHP also activates another member of the PPAR subfamily, PPARgamma. The effects of PPARalpha and PPARgamma activation in human breast cells appears to be opposing; PPARalpha activators in breast cells cause an increase in proliferation, while PPARgamma activation in breast cells is associated with differentiation and an inhibition of cell proliferation. Further to this the activation of the PPARs is cell and ligand specific, suggesting the importance of examining the effect of MEHP and MBP on the activation of PPARalpha, PPARbeta and PPARgamma in human breast. We used the common model of human breast cancer MCF-7 and examined the ability of MEHP and MBP to activate human PPARs in this system. The ability of MBP and MEHP to block PPAR responses was also assessed. We found that both human PPARalpha and PPARgamma were activated by MEHP whereas MEHP could not activate PPARbeta. MBP was unable to activate any PPAR isoforms in this breast model, despite being a weak peroxisome proliferator in liver, although MBP was an antagonist for both PPARgamma and PPARbeta. Our results suggest that the toxicological consequences of MEHP in the breast could be complex given the opposing effects of PPARalpha and PPARgamma in human breast cells.

Topics: Breast Neoplasms; Butyrates; Cell Differentiation; Cell Line, Tumor; Cell Proliferation; Diethylhexyl Phthalate; Dose-Response Relationship, Drug; Female; Humans; Phenylurea Compounds; Phthalic Acids; Plasticizers; PPAR alpha; PPAR gamma; PPAR-beta; Statistics, Nonparametric; Thiazoles; Thiazolidinediones; Transfection

The fatty-acid ethanolamide, oleoylethanolamide (OEA), is a naturally occurring lipid that regulates feeding and body weight [Rodriguez de Fonseca, F., Navarro, M., Gomez, R., Escuredo, L., Nava, F., Fu, J., Murillo-Rodriguez, E., Giuffrida, A., LoVerme, J., Gaetani, S., Kathuria, S., Gall, C., Piomelli, D., 2001. An anorexic lipid mediator regulated by feeding. Nature 414, 209-212], and serves as an endogenous agonist of peroxisome proliferator-activated receptor-alpha (PPAR-alpha) [Fu, J., Gaetani, S., Oveisi, F., Lo Verme, J., Serrano, A., Rodriguez De Fonseca, F., Rosengarth., A., Luecke, H., Di Giacomo, B., Tarzia, G., Piomelli, D., 2003. Oleoylethanolamide regulates feeding and body weight through activation of the nuclear receptor PPAR-alpha. Nature 425, 90-93], a ligand-activated transcription factor that regulates several aspects of lipid metabolism [. Peroxisome proliferator-activated receptors: nuclear control of metabolism. Endocr. Rev. 20, 649-688]). OEA reduces food intake in wild-type mice, but not in mice deficient in PPAR-alpha (PPAR-alpha(-/-)), an effect that is also observed with the PPAR-alpha agonists Wy-14643 and GW7647 [Brown, P.J., Chapman, J.M., Oplinger, J.A., Stuart, L.W., Willson, T.M. and Wu, Z., 2000. Chemical compounds as selective activators of PPAR-alpha. PCT Int. Appl., 32; . The PPARs: from orphan receptors to drug discovery. J. Med. Chem. 43, 527-550]. By contrast, specific agonists of PPAR-delta/beta (GW501516) or PPAR-gamma (ciglitazone) have no such effect. In obese Zucker rats, which lack functional leptin receptors, OEA reduces food intake and lowers body-weight gain along with plasma lipid levels. Similar effects are seen in diet-induced obese rats and mice. In the present study, we report that subchronic OEA treatment (5mgkg(-1), intraperitoneally, i.p., once daily for two weeks) in Zucker rats initiates transcription of PPAR-alpha and other PPAR-alpha target genes, including fatty-acid translocase (FAT/CD36), liver fatty-acid binding protein (L-FABP), and uncoupling protein-2 (UCP-2). Moreover, OEA decreases neutral lipid content in hepatocytes, as assessed by Oil red O staining, as well as serum cholesterol and triglyceride levels. The results suggest that OEA regulates lipid metabolism and that this effect may contribute to its anti-obesity properties.

Topics: Animals; Body Weight; Butyrates; CD36 Antigens; Cholesterol; Coenzyme A Ligases; Eating; Endocannabinoids; Fatty Acid-Binding Proteins; Hepatocytes; Hyperlipidemias; Ion Channels; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mitochondrial Proteins; Obesity; Oleic Acids; Phenylurea Compounds; PPAR alpha; Pyrimidines; Rats; Rats, Inbred WF; Rats, Zucker; RNA, Messenger; Thiazoles; Thiazolidinediones; Triglycerides; Uncoupling Protein 2