Resveratrol, a phytochemical inducer of multiple cell death pathways: apoptosis, autophagy and mitotic catastrophe

Cancers are the largest cause of mortality and morbidity in industrialized countries. In the field of the medicinal chemistry of natural products, numerous studies have reported interesting properties of trans-resveratrol as a chemopreventing agent against cancers, inflammation, and viral infection. Tumor growth inhibition has been linked to the ability of resveratrol to arrest cell cycle progression and to trigger cell death. This review focuses on the pathways that mediate resveratrol-induced cell death. Resveratrol impacts on the mitochondrial functions (respiratory chain, oncoproteins, gene expression, etc), in which p53 protein can be involved and its acetylated or phosphorylated forms. This polyphenol also affects death receptor distribution in ceramide-enriched membrane platforms which serve to trap and cluster receptor molecules, and facilitates the formation of a death-inducing signaling complex in the cell. To induce apoptosis, resveratrol also activates the ceramide / sphingomyelin pathway, which promotes ceramide generation and the downstream activation of kinase cascades. Resveratrol can activate alternative pathways to cell death such as those leading to autophagy, senescence or mitotic catastrophe. Furthermore, numerous attempts have been made using resveratrol analogs to improve the molecule's ability to block cell proliferation and induce cell death. Moreover, structural modification of natural phenolics is expected to produce analogs that may be useful tools to study the structure-activity relationships. Lastly, in various cancer types, resveratrol behaves as a chemosensitizer that lowers the threshold of cell death induction by classical anticancer agents and counteracts tumor cell chemoresistance.

The Peroxisomal 3-keto-acyl-CoA thiolase B Gene Expression Is under the Dual Control of PPARα and HNF4α in the Liver

PPARα and HNF4α are nuclear receptors that control gene transcription by direct binding to specific nucleotide sequences. Using transgenic mice deficient for either PPARα or HNF4α, we show that the expression of the peroxisomal 3-keto-acyl-CoA thiolase B (Thb) is under the dependence of these two transcription factors. Transactivation and gel shift experiments identified a novel PPAR response element within intron 3 of the Thb gene, by which PPARα but not HNF4α transactivates. Intriguingly, we found that HNF4α enhanced PPARα/RXRα transactivation from TB PPRE3 in a DNA-binding independent manner. Coimmunoprecipitation assays supported the hypothesis that HNF4α was physically interacting with RXRα. RT-PCR performed with RNA from liver-specific HNF4α-null mice confirmed the involvement of HNF4α in the PPARα-regulated induction of Thb by Wy14,643. Overall, we conclude that HNF4α enhances the PPARα-mediated activation of Thb gene expression in part through interaction with the obligate PPARα partner, RXRα.

Genetic-dependency of peroxisomal cell functions - emerging aspects

This paper reviews aspects concerning the genetic regulation of the expression of the well studied peroxisomal genes including those of fatty acid beta-oxidation enzymes; acyl-CoA oxidase, multifunctional enzyme and thiolase from different tissues and species. An important statement is PPARalpha, which is now long known to be in rodents the key nuclear receptor orchestrating liver peroxisome proliferation and enhanced peroxisomal beta-oxidation, does not appear to control so strongly in man the expression of genes involved in peroxisomal fatty acid beta-oxidation related enzymes. In this respect, the present review strengthens among others the emerging concept that, in the humans, the main genes whose expression is up-regulated by PPARalpha are mitochondrial and less peroxisomal genes. A special emphasis is also made on the animal cold adaptation and on need for sustained study of peroxisomal enzymes and genes; challenging that some essential roles of peroxisomes in cell function and regulation still remain to be discovered.

Human hepatic cell uptake of resveratrol: involvement of both passive diffusion and carrier-mediated process

This work reports significant advances on the transport in hepatic cells of resveratrol, a natural polyphenol with potent protective properties. First, we describe a new simple technique to qualitatively follow resveratrol cell uptake and intracellular distribution, based on resveratrol fluorescent properties. Second, the time-course study and the quantification of (3)H-labelled resveratrol uptake have been performed using human hepatic derived cells (HepG2 tumor cells) and hepatocytes. The temperature-dependence of the kinetics of uptake as well as the cis-inhibition experiments agree with the involvement of a carrier-mediated transport in addition to passive diffusion. The decrease of passive uptake resulting from resveratrol binding to serum proteins brings to light a mediated mechanism in physiological situation.

Peroxisome-proliferator-activated receptors as physiological sensors of fatty acid metabolism: molecular regulation in peroxisomes

The enzymes required for the beta-oxidation of fatty acyl-CoA are present in peroxisomes and mitochondria. Administration of hypolipidaemic compounds such as clofibrate to rodents leads to an increase in the volume and density of peroxisomes in liver cells. These proliferators also induce simultaneously the expression of genes encoding acyl-CoA oxidase, enoyl-CoA hydratase-hydroxyacyl-CoA dehydrogenase (multifunctional enzyme) and thiolase (3-ketoacyl-CoA thiolase). All these enzymes are responsible for long-chain and very-long-chain fatty acid beta-oxidation in peroxisomes. Similar results were observed when rat hepatocytes, or liver-derived cell lines, were cultured with a peroxisome proliferator. The increased expression of these genes is due to the stimulation of their transcription rate. These results show that the peroxisome proliferators act on the hepatic cells and regulate the transcription through various cellular components and pathways, including peroxisome-proliferator-activated receptor alpha (PPARalpha). After activation by specific ligands, either fibrates or fatty acid derivatives, PPARalpha binds to a DNA response element: peroxisome-proliferator-responsive element (PPRE), which is a direct repeat of the following consensus sequence: TGACCTXTGACCT, found in the promoter region of the target genes. PPARalpha is expressed mainly in liver, intestine and kidney. PPARalpha is a transcriptional factor, which requires other nuclear proteins for function including retinoic acid X receptor (RXRalpha) and other regulatory proteins. From our results and others we suggest the role of PPARalpha in the regulation of the peroxisomal fatty acid beta-oxidation. In this regard, we showed that although PPARalpha binds to thiolase B gene promoter at -681 to -669, a better response is observed with hepatic nuclear factor 4 ("HNf-4"). Moreover, rat liver PPARalpha regulatory activity is dependent on its phosphorylated state. In contrast, a protein-kinase-C-mediated signal transduction pathway seems to be modified by peroxisome proliferators, leading to an increase in the phosphorylation level of specific proteins, some of which have been shown to be involved in the phosphoinositide metabolism.

Relationship between signal transduction and PPAR alpha-regulated genes of lipid metabolism in rat hepatic-derived Fao cells

The goal of this study was to characterize phosphorylated proteins and to evaluate the changes in their phosphorylation level under the influence of a peroxisome proliferator (PP) with hypolipidemic activity of the fibrate family. The incubation of rat hepatic derived Fao cells with ciprofibrate leads to an overphosphorylation of proteins, especially one of 85 kDa, indicating that kinase (or phosphatase) activities are modified. Moreover, immunoprecipitation of 32P-labeled cell lysates shows that the nuclear receptor, PP-activated receptor, alpha isoform, can exist in a phosphorylated form, and its phosphorylation is increased by ciprofibrate. This study shows that PP acts at different steps of cell signaling. These steps can modulate gene expression of enzymes involved in fatty acid metabolism and lipid homeostasis, as well as in detoxication processes.

Properties of a fluorescent bezafibrate derivative (DNS-X). A new tool to study peroxisome proliferation and fatty acid beta-oxidation

The first peroxisome proliferator-activated receptor (PPAR) was cloned in 1990 by Issemann and Green. Many studies have reported the importance of this receptor in the control of gene expression of enzymes involved in lipid metabolic pathways including mitochondrial and peroxisomal fatty acid beta-oxidation, lipoprotein structure [apolipoprotein (apo) A2, apo CIII], and fatty acid synthase. By using radiolabeled molecules, it was shown that peroxisome proliferators bind and activate PPAR. As an alternative method, we developed a fluorescent dansyl (1-dimethylaminonaphthalene-5-sulfonyl) derivative peroxisome proliferator from bezafibrate (DNS-X), a hypolipidemic agent that exhibits an in vitro peroxisome proliferative activity on rat Fao-hepatic derived cultured cells. However, until now, the effect of this new compound on the liver of animals and subcellular localization was unknown. In addition to in vivo rat studies, we present a more efficient large-scale technique of DNS-X purification. Treating rats (DNS-X in the diet at 0.3% w/w) for 6 d leads to a hepatomegaly and a marked increase in liver peroxisomal palmitoyl-CoA oxidase activity. We also developed a method to localize and quantify DNS-X in tissues or cell compartment organelles. The primarily cytosolic distribution of DNS-X was confirmed by direct visualization using fluorescence microscopy of cultured Fao cells. Finally, transfection assay demonstrated that DNS-X enhanced the PPAR alpha activity as well as other peroxisome proliferators do.

Regulation of the peroxisomal beta-oxidation-dependent pathway by peroxisome proliferator-activated receptor alpha and kinases

The first PPAR (peroxisome proliferator-activated receptor) was cloned in 1990 by Issemann and Green (Nature 347:645-650). This nuclear receptor was so named since it is activated by peroxisome proliferators including several drugs of the fibrate family, plasticizers, and herbicides. This receptor belongs to the steroid receptor superfamily. After activation by a specific ligand, it binds to a DNA response element, PPRE (peroxisome proliferator response element), which is a DR-1 direct repeat of the consensus sequence TGACCT x TGACCT. This mechanism leads to the transcriptional activation of target genes (Motojima et al., J Biol Chem 273:16710-16714, 1998). After the first discovery, several isoforms were characterized in most of the vertebrates investigated. PPAR alpha, activated by hypolipidemic agents of the fibrate family or by leukotrienes; regulates lipid metabolism as well as the detoxifying enzyme-encoding genes. PPAR beta/delta, which is not very well known yet, appears to be more specifically activated by fatty acids. PPAR gamma (subisoforms 1, 2, 3) is activated by the prostaglandin PGJ2 or by antidiabetic thiazolidinediones (Vamecq and Latruffe, Lancet 354:411-418, 1999). This latter isoform is involved in adipogenesis. The level of PPAR expression is largely dependent on the tissue type. PPAR alpha is mainly expressed in liver and kidney, while PPAR beta/delta is almost constitutively expressed. In contrast, PPAR gamma is largely expressed in white adipose tissue. PPAR is a transcriptional factor that requires other nuclear proteins in order to function, i.e. RXRalpha (9-cis-retinoic acid receptor alpha) in all cases in addition to other regulatory proteins. Peroxisomes are specific organelles for very long-chain and polyunsaturated fatty acid catabolism. From our results and those of others, the inventory of the role of PPAR alpha in the regulation of peroxisomal fatty acid beta-oxidation is presented. In relation to this, we showed that PPAR alpha activates peroxisomal beta-oxidation-encoding genes such as acyl-CoA oxidase, multifunctional protein, and thiolase (Bardot et al., FEBS Lett 360:183-186, 1995). Moreover, rat liver PPAR alpha regulatory activity is dependent on its phosphorylated state (Passilly et al., Biochem Pharmacol 58:1001-1008, 1999). On the other hand, some signal transduction pathways such as protein kinase C are modified by peroxisome proliferators that increase the phosphorylation level of some specific proteins (Passilly et al. Eur J Biochem 230:316-321, 1995). From all these findings, PPAR alpha and kinases appear to play an important role in lipid homeostasis.

Evolutionary aspects of peroxisomes as cell organelles, and of genes encoding peroxisomal proteins

Peroxisomes are present in most eukaryotic cell types, and have different enzymatic content and metabolic functions throughout the life scale. The endosymbiotic origin of these DNA-devoid organelles is supported by evolutionary data concerning genes encoding not only most peroxisomal proteins, but also several transcriptional factors regulating their expression such as peroxisome proliferator-activated receptors.

Ciprofibrate stimulates protein kinase C-dependent phosphorylation of an 85 kDa protein in rat Fao hepatic derived cells

The effect of ciprofibrate on early events of signal transduction was previously studied in Fao cells. Protein kinase C (PKC) assays performed on permeabilized cells showed a more than two-fold increase in PKC activity in cells treated for 24 h with 500 microM ciprofibrate. To show the subsequent effect of this increase on protein phosphorylation, the in vitro phosphorylation on particulate fractions obtained from Fao cells was studied. Among several modifications, the phosphorylation of protein(s) with an apparent molecular mass of 85 kDa was investigated. This modification appeared in the first 24 h of treatment with 500 microM ciprofibrate. It was shown to occur on Ser/Thr residue(s). It was calcium but not calmodulin-dependent. The phosphorylation level of this/these protein(s) was reduced with kinase inhibitors and especially with 300 nM GF-109203X, a specific inhibitor of PKC. All these results suggest that the phosphorylation of the 85 kDa protein(s) is due to a PKC or to another Ser/Thr kinase activated via a PKC pathway. A possible biochemical candidate for 85 kDa protein seems to be the beta isoform of phosphatidylinositol 3-kinase regulatory subunit.

Inhibitory effect of resveratrol on the proliferation of human and rat hepatic derived cell lines

Resveratrol is a polyphenolic compound especially produced by grapevine and consequently found in wine. Based on epidemiological studies resveratrol may act as a cancer chemopreventive compound. The ability of resveratrol to inhibit cell proliferation was studied in rat hepatoma Fao cell line and human hepatoblastoma HepG2 cell line. The results show that resveratrol strongly inhibits cell proliferation at the micromolar range in a time- and dose-dependent manner. Concentrations higher than 50 microM become toxic. Fao cells are more sensitive than HepG2 cells. Interestingly, the presence of ethanol lowers the threshold of resveratrol effect. Resveratrol appears to prevent or to delay the entry to mitosis since no inhibition of [3H]thymidine incorporation is observed, while there is an increase of cell number in S and G2/M phases. In conclusion, resveratrol shows a strong inhibition of hepatic cell proliferation where alcohol may act as an enhancing agent.

Studies on regulation of the peroxisomal beta-oxidation at the 3-ketothiolase step. Dissection of the rat liver thiolase B gene promoter

The peroxisomal 3-oxoacyl-CoA thiolase (thiolase) is the last enzyme involved in the beta-oxidation of fatty acids. The enzyme cleaves long chain fatty acyl-CoA to generate acetyl-CoA and shortened acyl-CoA. The enzyme is nuclear encoded, synthesized in the cytoplasm and transported into peroxisomes. The thiolase B gene is inducible by the peroxisome proliferator compounds, like other genes involved in beta-oxidation of fatty acids in peroxisomes. The importance of studying thiolase is that it generates acetyl-CoA which is the precursor for the synthesis of molecules like cholesterol and fatty acids. The structural and functional analysis of thiolase at molecular level may add to the knowledge of fatty acid metabolism and further the obesity phenomenon. It is known that several genes mediate lipid homeostasis in target organs like liver, adipose tissue and are regulated by peroxisome proliferator activated receptors (PPAR alpha and PPAR gamma). To elucidate the mechanism of induction of rat liver thiolase B gene, an upstream 2.8 kb fragment containing promoter element has been subcloned and partially sequenced. The sequence analysis revealed a putative PPRE (Peroxisome Proliferator Response Element) of AGACCT T TGAACC sequence at -681 to -668 [Kliever et al. (1992) Nature 358:771-774]. By transient expression of a luciferase reporter gene in HeLa cells, we conclude that the identified PPRE could be functional in induction of thiolase B gene, but other sequences of genes might be involved.

The peroxisome proliferator response element (PPRE) present at positions -681/-669 in the rat liver 3-ketoacyl-CoA thiolase B gene functionally interacts differently with PPARalpha and HNF-4

Although previous data showed that the putative thiolase B PPRE located at -681/-669 bind the PPARalpha-RXRalpha heterodimer in vitro (Kliewer et al. (1992) Nature 358, 771-774), there is no evidence about the functional role of this element. By gel mobility-shift assay, we found an interaction of this PPRE with not only PPARalpha but also with HNF-4. By transfection of cells with the putative PPRE-driven luciferase reporter vector and PPARalpha, we found no significant activation of the luciferase gene expression, in contrast to the case with reporter expression driven by the PPRE of the peroxisomal bifunctional enzyme. On the other hand, HNF-4 activated the luciferase gene expression driven by the putative thiolase PPRE. We suggest that the thiolase B gene induction by peroxisome proliferators employs either another PPRE or this one in combination with other gene regulatory element(s) to lead to the strong gene expression observed in the presence of peroxisome proliferators.

Are physiological clonal expansion and maturation pathways a basis for discrepant behaviour of colon tumoral cell growth in response to the thiazolidinedione PPARgamma agonists?

Recently, anti-diabetic thiazolidinediones, pharmacological agonist ligands of peroxisome proliferator-activated receptor gamma (PPARgamma), have been shown to induce either protective or permissive effects towards colon epithelium tumoral cell growth. Several attractive explanations have been proposed but no final answer to these <conflicts in a nuclear family> is currently provided. It is not the purpose of the authors to bring this final answer but to offer another attractive hypothesis which might help our approach to explore further this exciting field of medical research.

Phosphorylation of peroxisome proliferator-activated receptor alpha in rat Fao cells and stimulation by ciprofibrate

The basic mechanism(s) by which peroxisome proliferators activate peroxisome proliferator-activated receptors (PPARs) is (are) not yet fully understood. Given the diversity of peroxisome proliferators, several hypotheses of activation have been proposed. Among them is the notion that peroxisome proliferators could activate PPARs by changing their phosphorylation status. In fact, it is well known that several members of the nuclear hormone receptor superfamily are regulated by phosphorylation. In this report, we show that the rat Fao hepatic-derived cell line, known to respond to peroxisome proliferators, exhibited a high content of PPARalpha. Alkaline phosphatase treatment of Fao cell lysate as well as immunoprecipitation of PPARalpha from cells prelabeled with [32P] orthophosphate clearly showed that PPARalpha is indeed a phosphoprotein in vivo. Moreover, treatment of rat Fao cells with ciprofibrate, a peroxisome proliferator, increased the phosphorylation level of the PPARalpha. In addition, treatment of Fao cells with phosphatase inhibitors (okadaic acid and sodium orthovanadate) decreased the activity of ciprofibrate-induced peroxisomal acyl-coenzyme A oxidase, an enzyme encoded by a PPARalpha target gene. Our results suggest that the gene expression controlled by peroxisome proliferators could be mediated in part by a modulation of the PPARalpha effect via a modification of the phosphorylation level of this receptor.

Medical significance of peroxisome proliferator-activated receptors

Peroxisome proliferator-activated receptors (PPAR) were discovered in 1990, ending 25 years of uncertainty about the molecular mechanisms of peroxisome proliferation. Subsequently, PPARs have improved our understanding of adipocyte differentiation. But there is more to PPARs than solving a puzzle about an organelle (the peroxisome) long considered an oddity, and their medical significance goes beyond obesity too. Enhanced PPAR type alpha expression protects against cardiovascular disorders though the role of enhanced PPARgamma expression seems less favourable. PPAR mechanisms, mainly via induction of more differentiated cell phenotypes, protect against some cancers. The differentiation of many cell types (hepatocyte, fibroblast, adipocyte, keratinocyte, myocyte, and monocyte/macrophage) involves PPARs, and these nuclear receptors are now attracting the attention of many medical specialties and the pharmaceutical industry.

Carcinogenic aspect of xenobiotic molecules belonging to the peroxisome proliferator family

It is known that a short-term exposure of rat, mice or incubation of hepatic cells with fibrate molecules leads to increase in peroxisome number and cell hyperplasia. Further, long-term incubation of cells (at least a year) show transformed characteristics with foci and nodules. To explain the hepatocarcinogenic effect of peroxisome proliferators in rodents we studied the effect of peroxisome proliferators on rat liver oncogenes expression. Earlier, we reported an increase in liver and kidney mRNA level of c-myc and N-myc. Since several metabolic genes are activated by PPAR (peroxisome proliferators activated receptor) through a PPRE (peroxisome proliferator response element), we suggest the involvment of PPAR in oncogene activation, because of the presence of PPRE in the N-myc 5'-upstream region. We showed by flow cytometric analysis that ciprofibrate increased the size of rat Fao derived cell line and the activity of palmitoyl CoA oxidase, a peroxisome proliferation enzyme marker for studying peroxisome proliferation was increased. The above effects which can contribute to hepatocarcinogenesis seem to be restricted to rat and mice, which show strong response to peroxisome proliferators. Indeed, no changes are observed in weak responsive species such as humans (using hepatic derived cell lines) and guinea pig. These data provide arguments for the non-carcinogenic effect of this xenobiotic class in human especially when sensitive, or normal individuals are exposed either to hypolipidaemic agents of the fibrate family.

Loss of response of carnitine palmitoyltransferase I to okadaic acid in transformed hepatic cells

The specific activity of carnitine palmitoyltransferase I (CPT-I) was similar in mitochondria isolated from rat Fao and human HepG2 hepatoma cells and from rat hepatocytes, but almost twofold higher in permeabilized hepatoma cells than in permeabilized hepatocytes. Short-term exposure to okadaic acid induced a ca. 80% stimulation of CPT-I in hepatocytes, whereas no significant response of the enzyme from hepatoma cells was evident. Thus, the high CPT-I activity displayed by hepatoma cells may be reached by hepatocytes upon challenge to okadaic acid. Reconstitution experiments with purified mitochondrial and cytoskeletal fractions showed that the cytoskeleton of hepatocytes produced a more remarkable inhibition of CPT-I than the cytoskeleton of Fao cells. The present data may be explained by a disruption of interactions between CPT-I and cytoskeletal components in tumor cells that may be involved in the okadaic acid-induced activation of hepatic CPT-I as previously suggested.

Expression of putative fatty acid transporter genes are regulated by peroxisome proliferator-activated receptor alpha and gamma activators in a tissue- and inducer-specific manner

Regulation of gene expression of three putative long-chain fatty acid transport proteins, fatty acid translocase (FAT), mitochondrial aspartate aminotransferase (mAspAT), and fatty acid transport protein (FATP), by drugs that activate peroxisome proliferator-activated receptor (PPAR) alpha and gamma were studied using normal and obese mice and rat hepatoma cells. FAT mRNA was induced in liver and intestine of normal mice and in hepatoma cells to various extents only by PPARalpha-activating drugs. FATP mRNA was similarly induced in liver, but to a lesser extent in intestine. The induction time course in the liver was slower for FAT and FATP mRNA than that of an mRNA encoding a peroxisomal enzyme. An obligatory role of PPARalpha in hepatic FAT and FATP induction was demonstrated, since an increase in these mRNAs was not observed in PPARalpha-null mice. Levels of mAspAT mRNA were higher in liver and intestine of mice treated with peroxisome proliferators, while levels in hepatoma cells were similar regardless of treatment. In white adipose tissue of KKAy obese mice, thiazolidinedione PPARgamma activators (pioglitazone and troglitazone) induced FAT and FATP more efficiently than the PPARalpha activator, clofibrate. This effect was absent in brown adipose tissue. Under the same conditions, levels of mAspAT mRNA did not change significantly in these tissues. In conclusion, tissue-specific expression of FAT and FATP genes involves both PPARalpha and -gamma. Our data suggest that among the three putative long-chain fatty acid transporters, FAT and FATP appear to have physiological roles. Thus, peroxisome proliferators not only influence the metabolism of intracellular fatty acids but also cellular uptake, which is likely to be an important regulatory step in lipid homeostasis.

Differential regulation by a peroxisome proliferator of the different multifunctional proteins in guinea pig: cDNA cloning of the guinea pig D-specific multifunctional protein 2

After our previous report on the cloning of two cDNA species in guinea pig, both encoding the same hepatic 79 kDa multifunctional protein 1 (MFP-1) [Caira, Cherkaoui-Malki, Hoefler and Latruffe (1996) FEBS Lett. 378, 57-60], here we report the cloning of a cDNA encoding a second multifunctional peroxisomal protein (MFP-2) in guinea-pig liver. This 2356 nt cDNA encodes a protein of 735 residues (79.7 kDa) whose sequence shows 83% identity with rat MFP-2 [Dieuaide-Noubhani, Novikov, Baumgart, Vanhooren, Fransen, Goethals, Vandekerckhove, Van Veldhoven and Mannaerts (1996) Eur. J. Biochem. 240, 660-666]. In parallel, we studied the effect of ciprofibrate, a hypolipaemic agent also known as peroxisome proliferator in rodent, on the expression of MFP-1 and MFP-2 (2.6 kb) in rats and guinea pigs. By Northern blotting analysis we demonstrated that three MFP-1-related mRNA species are expressed in the guinea-pig liver. The expression of two of them (3.5 and 2.6 kb) is slightly increased by ciprofibrate, whereas the 3.0 kb MFP-1 mRNA is, unlike the rat one, strongly down-regulated in guinea pigs treated with ciprofibrate. In a similar way, the hepatic expression of the guinea-pig 2.6 kb MFP-2 mRNA is also down-regulated in guinea pigs treated with ciprofibrate. These results demonstrate (1) that in contrast with the unique 3.0 kb MFP-1 rat mRNA, at least three hepatic MFP-1-related mRNA species are co-expressed in guinea pig; and (2) that, opposed to the accepted idea of non-responsiveness of the guinea pig to ciprofibrate, this drug affects MFP-1 and MFP-2 gene expression in this species. Also, the mRNA species for acyl-CoA oxidase and thiolase, two other enzymes of the peroxisomal beta-oxidation pathway that are induced severalfold in responsive species are down-regulated in guinea pig. This paper is the first, to our knowledge, reporting the down-regulation of the expression of genes encoding enzymes involved in the peroxisomal beta-oxidation of fatty acids (MFP-1) and bile acid synthesis (MFP-2) in mammals.

Peroxisome proliferators and peroxisome proliferator activated receptors (PPARs) as regulators of lipid metabolism

Peroxisome proliferation (PP) in mammalian cells, first described 30 years ago, represents a fascinating field of modern research. Major improvements made in its understanding were obtained through basic advances that have opened up new areas in cell biology, biochemistry and genetics. A decade after the first report on PP, a new metabolic pathway (peroxisomal beta-oxidation) and its inducibility by peroxisome proliferators were discovered. More recently, a new type of nuclear receptor, the peroxisome proliferator-activated receptor (PPAR), has been described. The first PPAR was discovered in 1990. Since then, many other PPARs have been characterized. This original class of nuclear receptors belongs to the superfamily of steroid receptors. With activation of cell signal transduction pathways, the occurrence of PPARs provides, for the first time, a coherent explanation of mechanisms by which PP is triggered. Nevertheless, although many compounds or metabolites are capable of activating PPARs, the natural direct ligands of these receptors have not been, up to now, clearly identified, with, however, the exception of 15-deoxy-12,14-prostaglandin J2 which is the ligand of PPAR gamma 2 while leukotrien LTB4 binds PPAR alpha. At this stage, the hypothesis of some orphan PPARs (ie receptors without known ligand) can not be ruled out. Despite these relatively restrictive aspects, the mechanisms by which activation of PPARs leads to PP become clear; also, coherent hypotheses among which a scenario involving receptor phosphorylation or a heat shock protein (ie HSP 72) can be proposed to explain how PPARs would be activated. The aim of this note is to review recent developments on PPARs, to present members up to now recognized to belong to the PPAR family, their characterization, functions, regulation and mechanisms of activation as well as their involvement in lipid metabolism regulation such as control of beta-oxidation, ketogenesis, fatty acid synthesis and lipoprotein metabolism. As an introducing section, a brief review of the major events between the first report of PP in mammals and the discovery of the first PPAR is given. Another section is devoted to current hypotheses on mechanisms responsible for PPAR activation and PP induction. Rather than an exhaustive presentation of cellular alterations accompanying PP induction, a dynamic overview of the lipid metabolism is provided. By assessing the biological significance of this organellar proliferative process, the reader will be led to conclude that the discovery of PPARs and related gene activation through peroxisome proliferator responsive element (PPRE) makes PP induction one of the most illustrative examples of control that occurs in lipid metabolism.

Preparation of a dansylated fibrate, a new fluorescent tool to study peroxisome proliferation. Effect on hepatic-derived cell lines

The synthesis of a dansylated fibrate (DNS-X) has been performed in order to identify the cellular affinity sites of peroxisome proliferators and to establish the subcellular localization of such molecules. DNS-X has been obtained by coupling the dansy1 chloride with the amine resulting from the bezafibrate alkaline hydrolysis. The purified DNS-X has been further characterized by spectrum analysis (UV-Vis, fluorescence, [1H]/[13C]-NMR and mass). At 250 microM and incubated for 48 h with the rat hepatic derived cells (Fao cells), DNS-X stimulates 12-fold the palmitoyl-CoA oxidase, a peroxisome proliferation marker enzyme. This increase is comparable to the one obtained with well known peroxisome proliferators such as bezafibrate or ciprofibrate. The stimulation by DNS-X is specific for the overall molecule since neither the dansyl chloride, the amine, nor the precursors of DNS-X are active. The increase of palmitoyl-CoA oxidase activity is correlated with the increase of the enzyme amount as shown by immunoblotting. In agreement with the species-specificity of the fibrate neither DNS-X, bezafibrate nor ciprofibrate significantly increase palmitoyl-CoA oxidase activity and the enzyme amount in human hepatic-derived cells, HepG2. This work shows that the dansylated fibrate is a new fluorescent tool to study the subcellular localization and identification of high affinity binding sites, then further on, to elucidate the peroxisome proliferation mechanism and the action of hypolipidaemic agents of the fibrate family.

Alkylation at the active site of the D-3-hydroxybutyrate dehydrogenase (BDH), a membrane phospholipid-dependent enzyme, by 3-chloroacetyl pyridine adenine dinucleotide (3-CAPAD)

The structure of the rat liver's D-3-hydroxybutyrate dehydrogenase (BDH) active site has been investigated using an affinity alkylating reagent, the 3-chloroacetyl pyridine adenine dinucleotide (3-CAPAD). This NAD+ analogue reagent strongly inactivates the enzyme following a concentration- and time-dependent process with a stoichiometry of approximately 1. The reagent reacts at the coenzyme binding site as revealed by the efficient protection by NADH. The effect of 3-CAPAD is stronger with the enzyme into its natural membrane environment than with the lipid-free purified apoBDH or with the reconstituted apoBDH-mitochondrial phospholipid complex. The pH-dependent effect on the inactivation process is in agreement with the participation of protons in the catalytic mechanism of BDH. Furthermore, this study exhibits the phospholipid activating role in BDH catalytic activation.

Properties of peroxisomes from jerboa (Jaculus orientalis)

This report presents new data on mammalian peroxisomes by studying an unusual rodent: the jerboa (Jaculus orientalis). This animal exhibits some unique peroxisomal properties compared to the rat, such as higher cyanide-insensitive palmitoyl-CoA oxidase specific activity, pattern differences in SDS-PAGE peroxisomal proteins as well as in acyl-CoA oxidase immunoblotting. There is also a peculiar response to a peroxisome proliferator, ciprofibrate. With 250 ppm of ciprofibrate in the diet for 2 weeks, we observed a limited liver peroxisome proliferation as well as a palmitoyl-CoA oxidase activity, enzyme content and mRNA increase. However, there was no increase in catalase activity, nor hepatomegaly which are prominent features of peroxisome proliferation in rats treated under the same conditions. The palmitoyl-CoA oxidase activity increase was weak in the kidney and not observed in the heart. Other subcellular organelle marker enzyme activities did not significantly change, especially the mitochondrial D-3-hydroxybutyrate and succinate dehydrogenases, lysosomal acid phosphatase, cytosolic lactate dehydrogenase and the endoplasmic reticulum NADPH-cytochrome c reductase. However, the activity of the liver membrane endoplasmic reticulum linked omega-lauryl hydroxylase (cytochrome P450 IV A1) increases after ciprofibrate treatment. Jerboa also behaves differently compared to the guinea pig after ciprofibrate treatment since the guinea pig has a weak response towards peroxisome proliferators. In conclusion, this first peroxisome study utilizing a different type of rodent as a laboratory animal, reveals that the jerboa shows unique peroxisome properties and responds in a moderate manner to a peroxisome proliferator, ciprofibrate, without leading to any increase in liver mass. This supports the fact that fibrate molecules may have different targets depending upon the species.

Human HepG2 and rat Fao hepatic-derived cell lines show different responses to ciprofibrate, a peroxisome proliferator: analysis by flow cytometry

Peroxisome proliferators, and especially hypolipidemic drugs such as ciprofibrate, are known to be hepatocarcinogens in rodents, but their effect in humans is controversial. In an attempt to investigate the effects of ciprofibrate at a cellular level, the analysis of individual whole cells was performed by flow cytometry on samples from two hepatic-derived cell lines: the rat Fao cell line and the human HepG2 cell line. The increase of light scatter signals in rat Fao cells treated for 3 days with ciprofibrate at 250 microM was related to modifications of intrinsic cellular parameters, such as size and cytoplasmic granularity. Conversely, no variations appeared in human HepG2-treated cells. Moreover, the study of the cell cycle distribution of asynchronously growing cells showed an increase in the percentage of proliferative cells in Fao-treated cells, but not in HepG2-treated cells. In order to give a simultaneous assessment of changes in cellular parameters and cell metabolism, these flow cytometric experiments were completed with the measurements of the palmitoyl-CoA oxidase activity, used as a marker of peroxisome proliferation. The cellular modifications in the rat Fao cell line were accompanied by a great increase in this enzymatic activity, whereas the human HepG2 cell line, which failed to exhibit changes of cytometric data, presented no, or weak, increase in this oxidase activity. The cellular modifications observed in the rat Fao cell line may be related to the well-known hepatocarcinogenicity of ciprofibrate in rodents, whereas the absence of response of HepG2 cells is in favor of the noncarcinogenicity of this drug in humans. This report validates another methodological approach for the investigation of the safety of peroxisome proliferators in humans.

Difference between guinea pig and rat in the liver peroxisomal response to equivalent plasmatic level of ciprofibrate

Guinea pig was previously classified as a species nonresponsive to peroxisome proliferators. However, none of the previous reports was based on pharmacokinetic data. Here, after a comparative pharmacokinetic study between the guinea pig and rat, we evaluate the guinea pig liver peroxisomal response to ciprofibrate, a hypolipemic agent and a potent peroxisome proliferator in rat. (1) Pharmacokinetic results show equivalent in guinea pig and rat when guinea pigs are treated with ciprofibrate at 30 mg/kg twice a day and rats are treated at 3 mg/kg once a day. (2) The treatment of guinea pigs at 30 mg/kg twice a day for 2 weeks leads to a significant increase in the liver peroxisomal palmitoyl-CoA oxidase activity (x 1.6) and also in the microsomal omega-laurate hydroxylase activity (x 1.8). These increases are in accordance with the changes in polypeptide patterns of isolated liver peroxisomes as well as in the immunoblotting of acyl-CoA oxidase. It is deduced that a weak, but significant, peroxisome proliferation can occur in guinea pig liver after a ciprofibrate treatment at dosages corresponding to equivalent plasmic concentrations of the drug between guinea pig and rat. (3) The hybridization of guinea pig liver RNA with the rat liver-inducible acyl-CoA oxidase cDNA probe shows a decrease in the corresponding heterologous mRNA content after treatment with ciprofibrate at 30 mg/kg twice a day. This result contrasts with the slight increase observed in immunodetection and in enzymatic assays, suggesting the existence of at least two different acyl-CoA oxidases in guinea pig liver peroxisomes.

Differential effects of nonhydroxylated flavonoids as inducers of cytochrome P450 1A and 2B isozymes in rat liver

Flavanone, flavone, and tangeretin differentially affected the activities of cytochrome P540 1A and 2B isozymes in rat liver. Flavone and, to a lesser extent, tangeretin, increased activities of ethoxyresorufin O-deethylase, methoxyresorufin O-demethylase, and pentoxyresorufin O-dealkylase (PROD), whereas flavanone mainly enhanced PROD activity. Immunoblot analysis indicated that flavone and tangeretin increased cytochrome P450 1A1, 1A2, and 2B1,2 forms, whereas flavanone only enhanced the cytochrome P450 2B isozymes. Northern blot study showed that flavone and tangeretin increased the level of the cytochrome P450 1A2 mRNAs. The concentration of the other mRNAs were slightly or not affected by flavonoids. These results suggest that the induction of P450 1A2 by flavone and tangeretin might involve a transcriptional and/or post-transcriptional mechanism.

Cloning and tissue expression of two cDNAs encoding the peroxisomal 2-enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase in the guinea pig liver

The 2-enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase (HD) is the second enzyme of the peroxisomal beta-oxidation pathway. In human and rat, only one HD mRNA has been so far detected in the liver. This paper reports for the first time in a mammal species, the guinea pig, the cloning and sequencing of two cDNAs encoding an HD. The 3,274 nucleotide-cDNA is a strictly identical but longer copy of the 2,494 nucleotide-form. A 2,178 bp-open reading frame encodes a protein of 726 amino acids (M(r) 79.3 kDa) with the peroxisomal-targeting signal (tripeptide SKL) at the carboxyterminus. Northern blot analysis of HD mRNA identified three mRNAs of respective sizes 3.5, 2.6 and 1.6 kb in the guinea pig liver and kidneys.

Stimulation of protein kinase C activity by compactin in vascular smooth muscle cells

The effect of compactin (a lovastatin analogue) on vascular smooth muscle cells was studied at the level of cell proliferation and protein kinase C. It was observed: a) an inhibition of cell proliferation by compactin at a micromolar range, which was prevented by simultaneous addition of mevalonate; b) a stimulation of DNA synthesis with a shift in the cell cycle kinetics, either in the presence or absence of fetal calf serum and c) an increase in protein kinase C activity in compactin-treated cells in the G1 phase of the cycle. This increase was similar to the one elicited by calyculin A, an inhibitor of protein phosphatases of type PP-1 and PP-2A. It is suggested that compactin behaves as a PP-1/PP-2A protein phosphatase inhibitor, inhibiting proliferation of smooth muscle cells by a block of the cell cycle after the S-phase.

Delayed effects of ciprofibrate on rat liver peroxisomal properties and proto-oncogene expression

Peroxisome proliferators (PPs) are non-genotoxic carcinogens in rodents. Their reversible effects on rat liver have been studied with ciprofibrate and fenofibrate. We found that with the hypolipemic drug fenofibrate a pause of 28 days is sufficient for a return to normal status, whereas with the highly potent PP ciprofibrate, the stimulation of ACO mRNA levels remains after its withdrawal. We investigated the effects of the renewal of the treatment with PPs on other peroxisomal parameters and proto-oncogene expression using Wistar rats. Interestingly, c-myc expression was enhanced even upon drug withdrawal, and was more stimulated by the second exposure to ciprofibrate, while c-fos expression was unaltered. However, only slight differences in c-Ha-ras expression were observed. Therefore, the effects of PPs in the Wistar rats are not totally reversible within 28 days following withdrawal, depending on the drug used. These delayed effects of ciprofibrate could be a key to our understanding the hepatocarcinogenic effect of PPs in rodents.

Influence of peroxisome proliferators on phosphoprotein levels in human and rat hepatic-derived cell lines

To elucidate the effect of peroxisome proliferators on the signal-transduction pathway, we have compared the effect of ciprofibrate, an hypolipaemic agent, on the overall phosphoprotein level between rat and human well differentiated hepatic derived cell lines. The phosphorylation status of several phosphoproteins in the rat Fao cell line was increased by the drug while no changes were observed in the human HepG2 cell line. In rat Fao cells, this increase, which is concentration and time dependent, can be as much as eightfold for 20-kDa and 22-kDa proteins. Wy-14,643, a non-fibrate molecule and a more potent peroxisome proliferator than ciprofibrate, increased the phosphorylation status of the same phosphoproteins. Peroxisome proliferators may act by activating kinases inactive in control cells, by amplifying kinases already active in control cells or by inactivating phosphatases. The phosphoamino acid residues affected are essentially serine and threonine. This modification of the signal-transduction pathway by the peroxisome proliferators in rodent cells appears to be an early event or an independent mechanism of the peroxisome proliferation. These results support the accumulating evidence that the perturbation of this pathway may be a major cause of the hepatomegaly and the hepatocarcinogenesis induced by peroxisome proliferators in rodent species. In contrast, the lack of phosphorylation changes in the human HepG2 cell line supports the non-toxic effect of peroxisome proliferators also used as hypolipaemic agents in humans.

Transcriptional and post-transcriptional analysis of peroxisomal protein encoding genes from rat treated with an hypolipemic agent, ciprofibrate. Effect of an intermittent treatment and influence of obesity

The treatment of rats with ciprofibrate, a potent peroxisome proliferator, led to increased levels of the peroxisomal acyl-CoA oxidase (ACO) mRNA. How ciprofibrate functions to elevate ACO mRNA is not known. To help determine the mechanism of ciprofibrate action, in vitro transcription assays were performed. It was determined that ciprofibrate was responsible for a 3.5-fold stimulation of the rate of ACO transcription within 24 hr of ingestion. It was also observed that the transcription rate stimulation following a 2-week ciprofibrate treatment of Wistar rats was maintained following 4 weeks of ciprofibrate withdrawal. Re-introduction of the drug after the 4-week pause resulted in greater stimulation than was initially observed. The results demonstrate that the effect of ciprofibrate is rapid and persists at least twice as long as the initial treatment period. In Zucker rats, both lean and obese, ACO mRNA levels were examined following 2 weeks of ciprofibrate treatment (1 or 3 mg/kg body weight/day). The presence of increased blood levels of triglycerides did not increase ciprofibrate action on transcription, although basal levels of transcription of peroxisomal enzymes were higher in obese rats. The increase in the ACO mRNA level was greater than the transcription rate stimulation suggesting a post-transcriptional regulation.

The analysis of modified peroxisome proliferator responsive elements of the peroxisomal bifunctional enzyme in transfected HepG2 cells reveals two regulatory motifs

Peroxisome proliferators (PPs) are non-genotoxic carcinogens in rodents. They can induce the expression of numerous genes via the heterodimerization of two members of the steroid hormone receptor superfamily, called the peroxisome proliferator-activated receptor (PPAR) and the 9-cis retinoic acid receptor (RXR). Many of the PP responsive genes possess a peroxisome proliferator response element (PPRE) formed by two TGACCT-related motifs. The bifunctional enzyme (HD) PPRE contains 3 such motifs, creating DR1 and DR2 sequences. PPAR and RXR regulate transcription via the DR1 element while DR2 modulates the expression of the gene via auxiliary factors in HepG2 cells.

Effect of peroxisomes proliferators and hypolipemic agents on mitochondrial inner membrane linked D-3-hydroxybutyrate dehydrogenase (BDH)

1. D-3-hydroxybutyrate dehydrogenase EC 1.1.1.30 (BDH) activity was measured in mitochondria of rats submitted to an intermittent feeding treatment with ciprofibrate or fenofibrate, i.e. fibrate analogues with hypolipemic activity and peroxisome proliferation properties. Our data shows an inhibition of rat liver mitochondrial BDH activity. This inhibitory effect is abolished when the treatment is stopped and reappears after a second treatment. 2. Incubation of hypolipemic agents (ciprofibrate, clofibrate, clobuzarit, fenofibrate or 2,4 dichlorophenoxyacetic acid) with submitochondrial linked BDH leads to an inhibition in a concentration dependent manner. 3. The protection by NAD(H) (coenzymes) and by methyl-malonate (a substrate analogue and competitive inhibitor) indicates that the inhibition occurs in the active site. On the other hand, there is a strong protection by phospholipid vesicles. This trapping effect may be attributed to lipophilic properties of hypolipemic agents. 4. Comparative effect of hypolipemic agents on mitochondrial BDH activity from rat liver and from Tetrahymena pyriformis indicates the same inhibition and same protection effects. This supports conservation of the enzymatic properties according to the evolution.

Histidyl phosphorylation of P36 in rat hepatoma Fao cells in vitro and in vivo

We have previously shown that a membrane-associated P36 from rat liver was in vitro phosphorylated at His residue(s) with a phosphoric amide bond (FEBS Lett., 319:75-79, 1993), and the activity was solubilized and partially purified (J. Biol. Chem., 269:9030-9037, 1994). The present study demonstrates that the P36 histidyl phosphorylation occurs in rat hepatoma cells under normal conditions. Phosphorylation and dephosphorylation of histidine as well as those of serine, threonine and tyrosine residues may also play an important role in animal cells.

Chemical reagents of polypeptides side chain: relationships between solubility properties and ability to cross the inner mitochondrial membrane

The correlation between the solubility properties of DCCD and EDAC (carboxyl specific groups reagents) and AI, NBD-Cl and TNM (tyrosyl specific reagents) and their efficiency to penetrate through the inner mitochondrial membrane, has been done. The penetration of the reagents was evaluated by using their ability to inactivate D-3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) in its natural location, i.e. in intact mitochondria, or in its inverted location, i.e. in inside-out submitochondrial vesicles. For DCCD, AI, NBD-Cl and TNM there is a good correlation between the phase partition in octanol/water and the ability to cross or not the inner mitochondrial membrane. In contrast, there is a discrepancy for EDAC reagent which is hydrophilic, while it significantly inhibits BDH in intact mitochondria. The knowledge of the properties of these reagents can be very useful to locate strategic aminoacid residues in important biological functions.

Monoclonal antibodies for structure-function studies of (R)-3-hydroxybutyrate dehydrogenase, a lipid-dependent membrane-bound enzyme

Monoclonal antibodies (mAbs) have been used to study structure-function relationships of (R)-3-hydroxybutyrate dehydrogenase (BDH) (EC 1.1.1.30), a lipid-requiring mitochondrial membrane enzyme with an absolute and specific requirement for phosphatidylcholine (PC) for enzymic activity. The purified enzyme (apoBDH, devoid of phospholipid and thereby inactive) can be re-activated with preformed phospholipid vesicles containing PC or by short-chain soluble PC. Five of six mAbs cross-react with BDH from bovine heart and rat liver, including two mAbs to conformational epitopes. One mAb was found to be specific for the C-terminal sequence of BDH and served to: (1) map endopeptidase cleavage and epitope sites on BDH; and (2) demonstrate that the C-terminus is essential for the activity of BDH. Carboxypeptidase cleavage of only a few (< or = 14) C-terminal amino acids from apoBDH (as detected by the loss of C-terminal epitope for mAb 3-10A) prevents activation by either bilayer or soluble PC. Further, for BDH in bilayers containing PC, the C-terminus is protected from carboxy-peptidase cleavage, whereas in bilayers devoid of PC the C-terminus is cleaved, and subsequent activation by PC is precluded. We conclude that: (1) the C-terminus of BDH is essential for enzymic activity, consistent with the prediction, from primary sequence analysis, that the PC-binding site is in the C-terminal domain of BDH; and (2) the allosteric activation of BDH by PC in bilayers protects the C-terminus from carboxypeptidase cleavage, indicative of a PC-induced conformational change in the enzyme.

Labeling of the mitochondrial membrane D-3-hydroxybutyrate dehydrogenase (BDH) with new bifunctional phospholipid analogues

D-3-Hydroxybutyrate dehydrogenase (BDH), an inner mitochondrial protein, is a well-known phospholipid dependent enzyme. It is a primary dehydrogenase of the oxidative phosphorylation system and is involved in the redox balance of the NAD+/NADH pool. The preparation of fluorescent phospholipids and newly synthesized bifunctional phospholipid analogues (fluorescent and photoactivatable) allowed us to study the structural requirement for lipid activation of the purified enzyme. This paper reports the chemical synthesis protocols to prepare these new phospholipids and their characterization. Illumination experiments of complexes between bifunctional phospholipids and BDH which lead to a cross-linked polypeptide indicate that both the polar head and the hydrophobic moiety of phospholipids interact with BDH. The bifunctional phospholipids were also tested on other lipid-binding proteins, i.e., horse cytochrome c and bovine serum albumin, and demonstrated the promising potential of this new type of photoactivatable molecules which can be followed merely by fluorescence without radioactive labeling.

PPAR-RXR heterodimer activates a peroxisome proliferator response element upstream of the bifunctional enzyme gene

A DNA sequence that confers a response to a class of rodent hepatocarcinogens termed peroxisome proliferators has been identified 2947bp upstream of the rat peroxisomal bifunctional enzyme gene. Two members of the steroid hormone receptor family, termed the peroxisome proliferator activated receptor (PPAR alpha) and the retinoid X receptor (RXR alpha), co-operate to bind specifically to this sequence. Importantly, this response element (PPRE) is similar to that identified upstream of other peroxisome proliferator responsive genes such as those encoding acyl CoA oxidase and cytochrome P450 IVA6. These data therefore provide further evidence that PPAR alpha plays an important role in mediating the action of peroxisome proliferators.

Role of thyroid state on induction by ciprofibrate of laurate hydroxylase and peroxisomal enzymes in rat liver microsomes

The effects of hypothyroidism and hyperthyroidism upon liver microsomal omega-laurate hydroxylase activity (cytochrome P450 IV A1-dependent), peroxisome proliferation marker enzyme activities and acyl CoA oxidase (AOX) expression induced by ciprofibrate (2 mg/kg/day during 8 days) were studied in the male Wistar rat so as to clarify firstly the possible involvement of thyroid hormones in the modification of peroxisomal ciprofibrate-induced enzyme activities in relation to hepatic microsomal cytochrome P450 IV A1 induction, and secondly the possible direct effect of thyroid hormones on the gene expression of specific peroxisomal enzymes. No significant change was found in the ciprofibrate-induced omega-laurate hydroxylase activity in hypothyroid rats or in rats that had received a large dose of triiodothyronine (LT3), suggesting that the thyroid hormone does not interfere with the peroxisome proliferation process through such an indirect mechanism. The induction by ciprofibrate [2-(4-(2-2dichlorocyclopropyl)phenoxyl-2methyl-propion ic acid)] of mitochondrial alpha-glycerolphosphate dehydrogenase and microsomal bilirubin UDPGT was decreased about 3-fold and 1.5-fold, respectively, while the induction of peroxisomal AOX, carnitine acetyl transferase and enoyl CoA hydratase enzyme activities was decreased by 36%, 34% and 22% in thyroidectomized animals, as compared to euthyroid animals. However, no significant changes in the quantity of peroxisomal proteins and in the AOX mRNA level were noted. The administration of large doses of LT3 to normal rats decreased the peroxisomal ciprofibrate AOX enzyme induction with a marked concomitant decrease in the AOX mRNA level. This suggests that high doses of LT3 enhance the turnover of some specific mRNAs or down regulate the peroxisome proliferator receptor. Our results also do not exclude inhibition of catabolic activity towards AOX which depends on thyroid hormone.

Biochemical properties of liver peroxisomes from rat, guinea pig and human species and the influence of hormonal status on rat liver acyl-CoA oxidase mRNA content

Liver peroxisomes from three different species, rat, guinea pig and man, have been purified by ultracentrifugation on a discontinuous Nycodenz gradient. Several biochemical parameters were tested in order to compare the basic peroxisomal properties of liver from rat, a species strongly responsive to peroxisome proliferators, and guinea pig and man, two weakly responsive species. Polypeptide patterns were compared and the bands in guinea pig and man comigrating with the two major bands in rat, catalase at 66 kDa and urate oxidase at 35 kDa, appeared in low amounts. However, other polypeptides are similar throughout these species especially in guinea pig as revealed by cross-immunoreactivity using an anti-rat peroxisomal protein rabbit immune serum. Specific activities of peroxisome acyl-CoA oxidase and microsome omega-lauryl hydroxylase have comparable rates in rat and guinea pig liver, but in human liver the activities are much lower. There is a cross-hybridization between acyl-CoA oxidase mRNA probed by rat liver acyl-CoA oxidase cDNA among the three species at a medium stringency. But interestingly, acyl-CoA oxidase mRNA from guinea pig and man appear to be larger in size. On the other hand, the hormonal status does not seem to have a significant effect on the rat liver acyl-CoA oxidase mRNA level suggesting at most that insulin, corticosterone and estradiol have no direct effect on acyl-CoA oxidase gene expression, which contrasts with the well-known effect of peroxisome proliferators.

Stimulation of peroxisomal palmitoyl-CoA oxidase activity by ciprofibrate in hepatic cell lines: comparative studies in Fao, MH1C1 and HepG2 cells

The response of two rat cell lines, Fao and MH1C1, and one human cell line, HepG2, to the peroxisome proliferator ciprofibrate, was studied. Using a fluorometric assay for palmitoyl-CoA oxidase, the dose- and time-dependent increase of this enzymatic activity was determined. From the lowest concentration (100 microM) stimulation is evident in the two rat cell lines. In the Fao line, the activity was stimulated reaching a seven-fold increase over the control level at 250 microM after 72 h of treatment. In the MH1C1 line, the maximum stimulation, four- to five-fold, was obtained at 250 and 500 microM after 72 h. In the HepG2 cell line, activity increased two-fold at 250 microM after 72 h reaching a three-fold increase at 1000 microM after 48 h. Ciprofibrate was more toxic to Fao cells than to MH1C1 and HepG2 cells which is also the order of the acyl-CoA oxidase stimulation by ciprofibrate. These preliminary results suggest that the two rat cell lines are appropriate for investigating the induction of peroxisomal beta-oxidation enzymes and the expression of their genes. The HepG2 cell line is a complementary model for the study of interspecies differences in the response to peroxisomal proliferators and of the peroxisomal functions implied in the lipid metabolism of human liver.

Expression of R-3-hydroxybutyrate dehydrogenase, a ketone body converting enzyme in heart and liver mitochondria of ruminant and non-ruminant mammals

1. The properties of rat liver and bovine heart R-3-hydroxybutyrate dehydrogenase (BDH) have been extensively studied in the past 20 years, but little is known concerning the biogenesis and the regulation of this dehydrogenase over different species. 2. In addition, controversial results were often reported concerning the activity, the level and the subcellular location of this enzyme in ruminants. 3. BDH activity found in liver and kidney mitochondria from ruminants (cow and sheep) is low, while it is much higher in rat. 4. However, the enzyme activity is detected in microsomes and in cytosol of liver and of kidney cells from ruminants. These activities are not correlated to ketonaemia level. 5. Although low BDH activity is detected in liver mitochondria from ruminants; the bovine liver BDH gene seems to be translated since BDH can be immunodetected by using an antiserum raised against bovine heart BDH. 6. Beside this, the good cross-reactivity between heart BDH and liver BDH suggests their high level of homology in ruminants.