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Title: PPAR{alpha} agonists up-regulate organic cation transporters in rat liver cells

Abstract

It has been shown that clofibrate treatment increases the carnitine concentration in the liver of rats. However, the molecular mechanism is still unknown. In this study, we observed for the first time that treatment of rats with the peroxisome proliferator activated receptor (PPAR)-{alpha} agonist clofibrate increases hepatic mRNA concentrations of organic cation transporters (OCTNs)-1 and -2 which act as transporters of carnitine into the cell. In rat hepatoma (Fao) cells, treatment with WY-14,643 also increased the mRNA concentration of OCTN-2. mRNA concentrations of enzymes involved in carnitine biosynthesis were not altered by treatment with the PPAR{alpha} agonists in livers of rats and in Fao cells. We conclude that PPAR{alpha} agonists increase carnitine concentrations in livers of rats and cells by an increased uptake of carnitine into the cell but not by an increased carnitine biosynthesis.

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [2]
  1. Institute of Agricultural and Nutritional Sciences, Martin-Luther-University Halle-Wittenberg, Emil-Abderhalden-Strasse 26, D-06108 Halle (Germany)
  2. Institute of Agricultural and Nutritional Sciences, Martin-Luther-University Halle-Wittenberg, Emil-Abderhalden-Strasse 26, D-06108 Halle (Germany). E-mail: klaus.eder@landw.uni-halle.de
Publication Date:
OSTI Identifier:
20854588
Resource Type:
Journal Article
Resource Relation:
Journal Name: Biochemical and Biophysical Research Communications; Journal Volume: 350; Journal Issue: 3; Other Information: DOI: 10.1016/j.bbrc.2006.09.099; PII: S0006-291X(06)02154-1; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; BIOSYNTHESIS; CARNITINE; CATIONS; ENZYMES; HEPATOMAS; LIVER; LIVER CELLS; RATS; RECEPTORS; UPTAKE

Citation Formats

Luci, Sebastian, Geissler, Stefanie, Koenig, Bettina, Koch, Alexander, Stangl, Gabriele I., Hirche, Frank, and Eder, Klaus. PPAR{alpha} agonists up-regulate organic cation transporters in rat liver cells. United States: N. p., 2006. Web. doi:10.1016/j.bbrc.2006.09.099.
Luci, Sebastian, Geissler, Stefanie, Koenig, Bettina, Koch, Alexander, Stangl, Gabriele I., Hirche, Frank, & Eder, Klaus. PPAR{alpha} agonists up-regulate organic cation transporters in rat liver cells. United States. doi:10.1016/j.bbrc.2006.09.099.
Luci, Sebastian, Geissler, Stefanie, Koenig, Bettina, Koch, Alexander, Stangl, Gabriele I., Hirche, Frank, and Eder, Klaus. Fri . "PPAR{alpha} agonists up-regulate organic cation transporters in rat liver cells". United States. doi:10.1016/j.bbrc.2006.09.099.
@article{osti_20854588,
title = {PPAR{alpha} agonists up-regulate organic cation transporters in rat liver cells},
author = {Luci, Sebastian and Geissler, Stefanie and Koenig, Bettina and Koch, Alexander and Stangl, Gabriele I. and Hirche, Frank and Eder, Klaus},
abstractNote = {It has been shown that clofibrate treatment increases the carnitine concentration in the liver of rats. However, the molecular mechanism is still unknown. In this study, we observed for the first time that treatment of rats with the peroxisome proliferator activated receptor (PPAR)-{alpha} agonist clofibrate increases hepatic mRNA concentrations of organic cation transporters (OCTNs)-1 and -2 which act as transporters of carnitine into the cell. In rat hepatoma (Fao) cells, treatment with WY-14,643 also increased the mRNA concentration of OCTN-2. mRNA concentrations of enzymes involved in carnitine biosynthesis were not altered by treatment with the PPAR{alpha} agonists in livers of rats and in Fao cells. We conclude that PPAR{alpha} agonists increase carnitine concentrations in livers of rats and cells by an increased uptake of carnitine into the cell but not by an increased carnitine biosynthesis.},
doi = {10.1016/j.bbrc.2006.09.099},
journal = {Biochemical and Biophysical Research Communications},
number = 3,
volume = 350,
place = {United States},
year = {Fri Nov 24 00:00:00 EST 2006},
month = {Fri Nov 24 00:00:00 EST 2006}
}
  • Species-differential toxic effects have been described with PPAR{alpha} and PPAR{gamma} agonists between rodent and human liver. PPAR{alpha} agonists (fibrates) are potent hypocholesterolemic agents in humans while they induce peroxisome proliferation and tumors in rodent liver. By contrast, PPAR{gamma} agonists (glitazones) and even dual PPAR{alpha}/{gamma} agonists (glitazars) have caused idiosyncratic hepatic and nonhepatic toxicities in human without evidence of any damage in rodent during preclinical studies. The mechanisms involved in such differences remain largely unknown. Several studies have identified the major target genes of PPAR{alpha} agonists in rodent liver while no comprehensive analysis has been performed on gene expression changes inducedmore » by PPAR{gamma} and dual PPAR{alpha}/{gamma} agonists. Here, we investigated transcriptomes of rat hepatocytes after 24 h treatment with two PPAR{gamma} (troglitazone and rosiglitazone) and two PPAR{alpha}/{gamma} (muraglitazar and tesaglitazar) agonists. Although, hierarchical clustering revealed a gene expression profile characteristic of each PPAR agonist class, only a limited number of genes was specifically deregulated by glitazars. Functional analyses showed that many genes known as PPAR{alpha} targets were also modulated by both PPAR{gamma} and PPAR{alpha}/{gamma} agonists and quantitative differences in gene expression profiles were observed between these two classes. Moreover, most major genes modulated in rat hepatocytes were also found to be deregulated in rat liver after tesaglitazar treatment. Taken altogether, these results support the conclusion that differential toxic effects of PPAR{alpha} and PPAR{gamma} agonists in rodent liver do not result from transcriptional deregulation of major PPAR target genes but rather from qualitative and/or quantitative differential responses of a small subset of genes.« less
  • Statins and fibrates (weak PPAR{alpha} agonists) are prescribed for the treatment of lipid disorders. Both drugs cause myopathy, but with a low incidence, 0.1-0.5%. However, combined statin and fibrate therapy can enhance myopathy risk. We tested the myotoxic potential of PPAR subtype selective agonists alone and in combination with statins in a differentiated rat myotube model. A pharmacologically potent experimental PPAR{alpha} agonist, Compound A, induced myotoxicity as assessed by TUNEL staining at a minimum concentration of 1 nM, while other weaker PPAR{alpha} compounds, for example, WY-14643, Gemfibrozil and Bezafibrate increased the percentage of TUNEL-positive nuclei at micromolar concentrations. In contrast,more » the PPAR{gamma} agonist Rosiglitazone caused little or no cell death at up to 10 {mu}M and the PPAR{delta} ligand GW-501516 exhibited comparatively less myotoxicity than that seen with Compound A. An experimental statin (Compound B) and Atorvastatin also increased the percentage of TUNEL-positive nuclei and co-treatment with WY-14643, Gemfibrozil or Bezafibrate had less than a full additive effect on statin-induced cell killing. The mechanism of PPAR{alpha} agonist-induced cell death was different from that of statins. Unlike statins, Compound A and WY-14643 did not activate caspase 3/7. In addition, mevalonate and geranylgeraniol reversed the toxicity caused by statins, but did not prevent the cell killing induced by WY-14643. Furthermore, unlike statins, Compound A did not inhibit the isoprenylation of rab4 or rap1a. Interestingly, Compound A and Compound B had differential effects on ATP levels. Taken together, these observations support the hypothesis that in rat myotube cultures, PPAR{alpha} agonism mediates in part the toxicity response to PPAR{alpha} compounds. Furthermore, PPAR{alpha} agonists and statins cause myotoxicity through distinct and independent pathways.« less
  • The synthesis of a new series of phenylpropanoic acid derivatives incorporating an heteroaryl group at the {alpha}-position and their evaluation for binding and activation of PPAR{alpha} and PPAR{gamma} are presented in this report. Among the new compounds, (S)-3-{l_brace}4-[3-(5-methyl-2-phenyl-oxazol-4-yl)-propyl]-phenyl{r_brace}-2-1,2,3-triazol-2-yl-propionic acid (17j), was identified as a potent human PPAR{alpha}/{gamma} dual agonist (EC{sub 50} = 0.013 and 0.061 {micro}M, respectively) with demonstrated oral bioavailability in rat and dog. 17j was shown to decrease insulin levels, plasma glucose, and triglycerides in the ZDF female rat model. In the human apolipoprotein A-1/CETP transgenic mouse model 17j produced increases in hApoA1 and HDL-C and decreases inmore » plasma triglycerides. The increased potency for binding and activation of both PPAR subtypes observed with 17j when compared to previous analogs in this series was explained based on results derived from crystallographic and modeling studies.« less
  • PPAR{gamma} agonists inhibit liver fibrosis, but the mechanisms involved are uncertain. We hypothesized that PPAR{gamma} agonists inhibit transforming growth factor (TGF){beta}1-activation of TGF{beta} receptor (TGF{beta}R)-1 signaling in quiescent stellate cells, thereby abrogating Smad3-dependent induction of extracellular matrix (ECM) genes, such as PAI-1 and collagen-1{alpha}I. To test this, human HSC were cultured to induce a quiescent phenotype, characterized by lipid accumulation and PPAR{gamma} expression and transcriptional activity. These adipocytic HSC were then treated with TGF{beta}1 {+-} a TGF{beta}R-1 kinase inhibitor (SB431542) or a PPAR{gamma} agonist (GW7845). TGF{beta}1 caused dose- and time-dependent increases in Smad3 phosphorylation, followed by induction of collagen andmore » PAI-1 expression. Like the TGF{beta}R-1 kinase inhibitor, the PPAR{gamma} agonist caused dose-dependent inhibition of all of these responses without effecting HSC proliferation or viability. Thus, the anti-fibrotic actions of PPAR{gamma} agonists reflect their ability to inhibit TGF{beta}1-TGF{beta}R1 signaling that initiates ECM gene expression in quiescent HSC.« less
  • Although non-alcoholic fatty liver disease (NAFLD) is currently the most common form of chronic liver disease there is no pharmacological agent approved for its treatment. Since peroxisome proliferator-activated receptors (PPARs) are closely associated with hepatic lipid metabolism, they seem to play important roles in NAFLD. However, the effects of PPAR agonists on steatosis that is a common pathology associated with NAFLD, remain largely controversial. In this study, the effects of various PPAR agonists, i.e. fenofibrate, bezafibrate, troglitazone, rosiglitazone, muraglitazar and tesaglitazar on oleic acid-induced steatotic HepaRG cells were investigated after a single 24-hour or 2-week repeat treatment. Lipid vesicles stainedmore » by Oil-Red O and triglycerides accumulation caused by oleic acid overload, were decreased, by up to 50%, while fatty acid oxidation was induced after 2-week co-treatment with PPAR agonists. The greatest effects on reduction of steatosis were obtained with the dual PPARα/γ agonist muraglitazar. Such improvement of steatosis was associated with up-regulation of genes related to fatty acid oxidation activity and down-regulation of many genes involved in lipogenesis. Moreover, modulation of expression of some nuclear receptor genes, such as FXR, LXRα and CAR, which are potent actors in the control of lipogenesis, was observed and might explain repression of de novo lipogenesis. Conclusion: Altogether, our in vitro data on steatotic HepaRG cells treated with PPAR agonists correlated well with clinical investigations, bringing a proof of concept that drug-induced reversal of steatosis in human can be evaluated in in vitro before conducting long-term and costly in vivo studies in animals and patients. - Highlights: • There is no pharmacological agent approved for the treatment of NAFLD. • This study demonstrates that PPAR agonists can reduce fatty acid-induced steatosis. • Some nuclear receptors appear to be potent actors in the control of lipogenesis. • A proof of concept that reversal of steatosis can be evaluated in human HepaRG cells.« less