Liver gene expression in rats in response to the peroxisome proliferator-activated receptor-alpha agonist ciprofibrate (original) (raw)
Related papers
2006
Background: Fibrates are a unique hypolipidemic drugs that lower plasma triglyceride and cholesterol levels through their action as peroxisome proliferator-activated receptor alpha (PPARα) agonists. The activation of PPARα leads to a cascade of events that result in the pharmacological (hypolipidemic) and adverse (carcinogenic) effects in rodent liver. Results: To understand the molecular mechanisms responsible for the pleiotropic effects of PPARα agonists, we treated mouse primary hepatocytes with three PPARα agonists (bezafibrate, fenofibrate, and WY-14,643) at multiple concentrations (0, 10, 30, and 100 μM) for 24 hours. When primary hepatocytes were exposed to these agents, transactivation of PPARα was elevated as measured by luciferase assay. Global gene expression profiles in response to PPARα agonists were obtained by microarray analysis. Among differentially expressed genes (DEGs), there were 4, 8, and 21 genes commonly regulated by bezafibrate, fenofibrate, and WY-14,643 treatments across 3 doses, respectively, in a dose-dependent manner. Treatments with 100 μM of bezafibrate, fenofibrate, and WY-14,643 resulted in 151, 149, and 145 genes altered, respectively. Among them, 121 genes were commonly regulated by at least two drugs. Many genes are involved in fatty acid metabolism including oxidative reaction. Some of the gene changes were associated with production of reactive oxygen species, cell proliferation of peroxisomes, and hepatic disorders. In addition, 11 genes related to the development of liver cancer were observed. Conclusion: Our results suggest that treatment of PPARα agonists results in the production of oxidative stress and increased peroxisome proliferation, thus providing a better understanding of mechanisms underlying PPARα agonist-induced hepatic disorders and hepatocarcinomas.
Toxicology and Applied Pharmacology, 1998
The regulation of gene expression via the peroxisome proliferator-activated receptor (PPAR) is believed to be critical in the effects of peroxisome proliferators on lipid metabolism and possibly in hepatocarcinogenesis. The involvement of PPAR in the peroxisome proliferator-mediated induction of fatty acid metabolizing genes such as acyl-CoA oxidase (ACO), fatty acid-binding protein (FABP), and cytochrome P450IVA1 (CYP4A1) has been clearly demonstrated. However, the induction by peroxisome proliferators of important growth regulatory genes such as c-myc has not been investigated extensively. In these studies we examined the dose-response relationships for the induction of mRNA for the PPAR-regulated and lipid metabolizing genes ACO, FABP, and CYP4A1 and compared them to the immediate early gene c-myc. Liver mRNA from rats fed various amounts of the peroxisome proliferator Wy14,643 for 13 weeks was utilized. The lipid metabolism and growth regulatory genes were induced by subchronic administration of Wy14,643 but to varying degrees and with different sensitivities. The lowest dose that resulted in a significant change in ACO and FABP expression was 10 ppm. The mRNA for CYP4A1 and c-myc was significantly affected at the lowest dose examined (5 ppm). Also, the maximal induction ranged from 10 5-fold (CYP4A1) to less than 10-fold (FABP) relative to vehicle-treated animals. The accumulation of mRNA for ACO, FABP, and CYP4A1, but not c-myc, showed typical receptormediated dose-response relationships. The effects on gene expression were compared to rates of hepatic cell proliferation, a pertinent marker of tumor promotion and hepatocarcinogen-esis. Surprisingly, ACO mRNA showed an excellent correlation (r 2 ؍ 0.9) while c-myc mRNA exhibited a poor correlation (r 2 ؍ 0.3) with cell proliferation in rat liver. Although the differences between the dose-response relationships of ACO and c-myc mRNA accumulation may suggest immediate early genes are not controlled by PPAR, evidence from PPAR␣ null mice support this receptor in both lipid metabolism and growth regulatory genes. This study shows the complexity of responses mediated by peroxisome proliferators, with ACO being a good marker of PPAR-mediated events as well as cell proliferation, while c-myc, a known growth regulatory gene, was induced by Wy14,643 partially via PPAR but did not correlate well with cell proliferation.
Protein Profiling of Mouse Livers with Peroxisome Proliferator-Activated Receptor Activation
Molecular and Cellular Biology, 2004
Peroxisome proliferator-activated receptor ␣ (PPAR␣) is important in the induction of cell-specific pleiotropic responses, including the development of liver tumors, when it is chronically activated by structurally diverse synthetic ligands such as Wy-14,643 or by unmetabolized endogenous ligands resulting from the disruption of the gene encoding acyl coenzyme A (CoA) oxidase (AOX). Alterations in gene expression patterns in livers with PPAR␣ activation were delineated by using a proteomic approach to analyze liver proteins of Wy-14,643-treated and AOX ؊/؊ mice. We identified 46 differentially expressed proteins in mouse livers with PPAR␣ activation. Up-regulated proteins, including acetyl-CoA acetyltransferase, farnesyl pyrophosphate synthase, and carnitine O-octanoyltransferase, are involved in fatty acid metabolism, whereas down-regulated proteins, including ketohexokinase, formiminotransferase-cyclodeaminase, fructose-bisphosphatase aldolase B, sarcosine dehydrogenase, and cysteine sulfinic acid decarboxylase, are involved in carbohydrate and amino acid metabolism. Among stress response and xenobiotic metabolism proteins, selenium-binding protein 2 and catalase showed a dramatic ϳ18-fold decrease in expression and a modest ϳ6-fold increase in expression, respectively. In addition, glycine N-methyltransferase, pyrophosphate phosphohydrolase, and protein phosphatase 1D were down-regulated with PPAR␣ activation. These observations establish proteomic profiles reflecting a common and predictable pattern of differential protein expression in livers with PPAR␣ activation. We conclude that livers with PPAR␣ activation are transcriptionally geared towards fatty acid combustion.
European Journal of Biochemistry, 1993
Ciprofibrate, a hypolipidaemic drug with carcinogenic and peroxisome-proliferation effects in rat liver, was found to increase the phosphorylation of epidermal-growth-factor receptor in 32Plabeled isolated rat hepatocytes. This effect was suppressed by protein-kinase-C inhibitors, and was accompanied by an almost complete inhibition of the receptor autophosphorylation normally induced by its ligand. However, in vitro experiments showed that protein-kinase-C phosphorylation of purified epidermal-growth-factor receptor was activated by ciprofibroyl-CoA, the acyl-CoA derivative of the drug, but not by the unmodified drug. Neither compound affected the ligand induction of epidermal-growth-factor-receptor autophosphorylation in isolated liver membranes. These results suggest that metabolically produced ciprofibroyl-CoA in liver cells would activate protein-kinase-C and produce changes in epidermal-growth-factor-receptor function.
FEBS Letters, 1989
Using the normal adult rat hepatocytes, plated on rat tail collagen‐coated dishes and fed a chemically defined medium, we demonstrate here that ciprofibrate at 0.1 mM concentration, increases significantly the mRNA levels of fatty acyl‐CoA oxidase, enoyl‐CoA hydratase/3‐hydroxyacyl‐CoA dehydrogenase bifunctional protein, and thiolase (the three enzymes of the β‐oxidation system), and causes peroxisome proliferation. Increase in mRNA levels of these genes was evident within 1 h and was maximal 24 h after the addition of ciprofibrate. In hepatocytes cultured in the absence of ciprofibrate, the basal levels of these enzymes were low and further declined with time. Concomitant treatment of hepatocytes with cycloheximide did not inhibit or superinduce the mRNA levels, indicating that this induction may represent a primary (direct) effect of this compound on the expression of these genes and does not apparently involve short‐lived repressor protein(s).
Genes involved in the induction of liver growth by peroxisome proliferators
Toxicology Research, 2014
The mechanisms regulating the induction of hepatic DNA synthesis by PPARα agonists are currently incompletely understood, and we set out to determine whether there are different mechanisms of induction for PPARα agonists and other hepatic growth agents. High levels of hepatic DNA synthesis (3-7%) were induced by a PPARα agonist, ciprofibrate, and by a PXRα agonist, cyproterone acetate, and liver samples were taken for transcriptomic analysis in a contemporaneous experiment. Microarray analysis of tissue RNAs detected gene induction at 24 hours after dosing, but failed to detect any biologically plausible response at 1-5 hours after dosing. RNA sequencing of control and ciprofibrate samples at 3 hours after dosing revealed 527 perturbed genes, including known PPARα target genes. Seven candidate genes of interest in regulating cell growth and apoptosis were examined by RT-PCR, and were confirmed to be induced by ciprofibrate treatment. Cyproterone acetate, TCPOBOP and partial hepatectomy induced a distinct spectrum of gene induction for ciprofibrate, demonstrating that ciprofibrate induces DNA synthesis through a unique mechanism. These data show that RNA sequencing is a powerful tool for analysis of differentially induced genes in rat liver, and for identification of candidate genes that mediate the induction of DNA synthesis by PPARα agonists.
Journal of Molecular Endocrinology, 2003
Peroxisome proliferator activated receptor (PPAR)-alpha controls the expression of multiple genes involved in lipid metabolism, and activators of PPAR-alpha, such as fibrates, are commonly used drugs in the treatment of hypertriglyceridemia and other dyslipidemic states. Recent data have also suggested a role for PPAR-alpha in insulin resistance and glucose homeostasis. In the present study, we have assessed the transcriptional and physiological responses to PPAR-alpha activation in a diet-induced rat model of insulin resistance. The two PPAR-alpha activators, fenofibrate and Wy-14643, were dosed at different concentrations in high-fat fed Sprague-Dawley rats, and the transcriptional responses were examined in liver using cDNA microarrays. In these analyses, 98 genes were identified as being regulated by both compounds. From this pool of genes, 27 correlated to the observed effect on plasma insulin, including PPAR-alpha itself and the leukocyte antigen-related protein tyrosine phosp...
Archives of Toxicology, 2001
Peroxisome proliferators (PPs) are a diverse group of chemicals that cause hepatic proliferation, suppression of apoptosis, peroxisome proliferation and liver tumours in rodents. The biochemical response to PPs involves changes in the expression of peroxisomal b-oxidation enzymes and fatty acid transport proteins such as acyl-CoA oxidase and liver fatty acid binding protein. The response to PPs is mediated by the peroxisome proliferator-activated receptor a (PPARa) and the livers of PPARa-null transgenic mice do not develop tumours in response to PPs. In order to identify the molecular pathways underlying the adverse eects of PPs in rodent liver, we carried out two-dimensional dierential gel electrophoresis to provide quantitative proteomic analyses of diethylhexylphthalate (DEHP)treated wild-type or PPARa-null mouse livers. Since tumourigenesis is both PP-and PPARa-dependent, analyses were focused on these changes. Fifty-nine proteins were identi®ed where altered expression was both PPARa-and PP-dependent. In addition, six proteins regulated by the deletion of PPARa were identi®ed, possibly indicating an adaptive change in response to the loss of this receptor. The proteins that we identi®ed as being regulated by PPARa are known to be involved in lipid metabolism pathways, but also in amino acid and carbohydrate metabolism, mitochondrial bioenergetics and in stress responses including several genes not previously reported to be regulated by PPARa. These data provide novel insights into the pathways utilised by PPs and may assist in the identi®cation of early markers rodent nongenotoxic hepatocarcinogenesis.
Gene Expression Profiling of the PPAR-alpha Agonist Ciprofibrate in the Cynomolgus Monkey Liver
Toxicological Sciences, 2005
Fibrates, such as ciprofibrate, fenofibrate, and clofibrate, are peroxisome proliferator-activated receptor-a (PPARa) agonists that have been in clinical use for many decades for treatment of dyslipidemia. When mice and rats are given PPARa agonists, these drugs cause hepatic peroxisome proliferation, hypertrophy, hyperplasia, and eventually hepatocarcinogenesis. Importantly, primates are relatively refractory to these effects; however, the mechanisms for the species differences are not clearly understood. Cynomolgus monkeys were exposed to ciprofibrate at various dose levels for either 4 or 15 days, and the liver transcriptional profiles were examined using Affymetrix human GeneChips. Strong upregulation of many genes relating to fatty acid metabolism and mitochondrial oxidative phosphorylation was observed; this reflects the known pharmacology and activity of the fibrates. In addition, (1) many genes related to ribosome and proteasome biosynthesis were upregulated, (2) a large number of genes downregulated were in the complement and coagulation cascades, (3) a number of key regulatory genes, including members of the JUN, MYC, and NFkB families were downregulated, which appears to be in contrast to the rodent, where JUN and MYC are reported to upregulated after PPARa agonist treatment, (4) no transcriptional signal for DNA damage or oxidative stress was observed, and (5) transcriptional signals consistent with an antiproliferative and a pro-apoptotic effect were seen. We also compared the primate data to literature reports of hepatic transcriptional profiling in PPARa-treated rodents, which showed that the magnitude of induction in b-oxidation pathways was substantially greater in the rodent than the primate.