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Ruth A. Roberts - One of the best experts on this subject based on the ideXlab platform.
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Suppression of Liver Cell Apoptosis In Vitro by the
2013Co-Authors: Non-genotoxic Hepatocarcinogen, Ruth A. Roberts, Alison C. Bayly, Peroxisome Proliferator Nafenopin, Caroline DiveAbstract:Abstract. Suppression of apoptosis has been implicated as a mechanism for the hepatocarcinogenicity of the peroxisome proliferator class of non-genotoxic carcinogens. The ability of the peroxisome proliferator Nafenopin to suppress or delay the onset of liver apoptosis was investigated using primary cultures of rat hepatocytes and the Reuber hepatoma cell line FaO. 50 ~M Nafenopin reversibly maintained the viability of primary rat hepatocyte cultures which otherwise degenerated within 8 d of establishment. The maintenance of viability of hepatoeyte monolayers was associated with a significant decrease in the number of cells exhibiting chromatin condensation patterns typical of apoptosis. Apoptosis could be induced in hepatocytes by administration of 5 ng/ml TGFBt. Coadditio
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Role of hepatic non-parenchymal cells in the response of rat hepatocytes to the peroxisome proliferator Nafenopin in vitro
Carcinogenesis, 2000Co-Authors: Susan C. Hasmall, Douglas A. West, Kine Olsen, Ruth A. RobertsAbstract:Induction of liver cancer by peroxisome proliferators such as Nafenopin is frequently associated with increased liver growth, increased DNA synthesis and suppression of apoptosis. The cytokine, tumour necrosis factor alpha (TNF alpha), and non-parenchymal liver cells have been implicated in mediating the hepatic response to peroxisome proliferators. Here, we have investigated the dependency of the hepatocyte response to peroxisome proliferators on non-parenchymal cells, a major source of hepatic cytokines. Addition of non-parenchymal cells, or conditioned medium from non-parenchymal cell cultures, increased DNA synthesis (220% and 270% of control, respectively) and suppressed transforming growth factor beta(1)-induced hepatocyte apoptosis (32% and 54% of control, respectively). Removal of non-parenchymal cells from normal hepatocyte cultures prevented both the Nafenopin- and TNF alpha-induced increase in DNA synthesis and suppression of hepatocyte apoptosis; this response was restored by returning non-parenchymal cells to the purified hepatocytes. TNF alpha was detected in the medium of non-parenchymal cell (3-15 pg/ml) and normal hepatocyte cultures (25-100 pg/ml) by bioassay using L929 cells. However, the contribution of TNF alpha released from non-parenchymal cells was small compared with that released spontaneously by hepatocytes. Nafenopin significantly increased the release of TNF alpha from non-parenchymal cells to 56 +/- 18 pg/ml, but had little effect on TNF alpha release by hepatocytes. However, the concentration of exogenous TNF alpha required to elicit a response in hepatocytes was 100 pg/ml and above. These data provide evidence that hepatic non-parenchymal cells are permissive for the growth response of hepatocytes in vitro to peroxisome proliferators and this may be mediated, at least in part by TNF alpha. However, the levels of TNF alpha released spontaneously or in response to peroxisome proliferators are insufficient per se to induce a growth response.
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Role of MAP kinase signalling pathways in the mode of action of peroxisome proliferators
Carcinogenesis, 2000Co-Authors: Sabina Cosulich, Neil H. James, Ruth A. RobertsAbstract:Peroxisome proliferators (PPs) are a class of non-genotoxic chemicals that cause rodent liver enlargement and hepatocarcinogenesis. In primary rat hepatocytes, PPs cause cell proliferation, suppression of apoptosis and peroxisome proliferation. We have investigated the role of different families of mitogen-activated protein (MAP) kinases in the mode of action of PPs. Addition of 50 microM Nafenopin to primary rat hepatocyte cultures caused weak activation of extracellular signal regulated kinases and p38 MAP kinase. However, incubation of primary hepatocytes with the p38 MAP kinase inhibitor SB203580 or the MAP kinase kinase (MEK) inhibitor PD098059 prevented the induction of DNA synthesis and the suppression of transforming growth factor beta(1)-induced apoptosis by the PP Nafenopin. In contrast, in the presence of these MAP kinase inhibitors, Nafenopin still induced palmitoyl CoA oxidation, a measure of peroxisome proliferation. We have shown previously that PPs such as Nafenopin require tumour necrosis factor alpha (TNF-alpha) to exert their effects on cellular proliferation and apoptosis. Here we show that treatment of primary rat hepatocyte cultures with Nafenopin causes an increase in bioactive TNF-alpha and that this process requires p38 MAP kinase activity.
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Proteomic analysis of differential protein expression in primary hepatocytes induced by EGF, tumour necrosis factor α or the peroxisome proliferator Nafenopin
European journal of biochemistry, 2000Co-Authors: Stephan Chevalier, Neil Macdonald, Robert Tonge, Steve Rayner, Rachel Rowlinson, Joanne Shaw, Janice Young, Matthew Davison, Ruth A. RobertsAbstract:Peroxisome proliferators are nongenotoxic rodent-liver carcinogens that have been shown to cause both an induction of hepatocyte proliferation and a suppression of apoptosis. Both epidermal growth factor (EGF) and the peroxisome proliferator Nafenopin induce DNA replication in primary rat hepatocyte cultures, but apparently through different signalling pathways. However, both EGF and Nafenopin require tumour necrosis factor alpha (TNFalpha) signalling to induce DNA replication. By examining proteins isolated from rat primary hepatocyte cultures using two-dimensional gel electrophoresis and mass spectrometry, we found that proteins showing an altered expression pattern in response to Nafenopin differed from those showing altered expression in response to EGF. However, many proteins showing altered expression upon stimulation with TNFalpha were common to both the EGF and Nafenopin responses. These proteome profiling experiments contribute to a better understanding of the molecular mechanisms involved in the response to peroxisome proliferators. We found 32 proteins with altered expression upon stimulation with Nafenopin, including muscarinic acetylcholine receptor 3, intermediate filament vimentin and the beta subunit of the ATP synthase. These nonperoxisomal protein targets offer insights into the mechanisms of peroxisome proliferator-induced carcinogenesis in rodents and provide opportunities to identify toxicological markers to facilitate early identification of nongenotoxic carcinogens.
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Tumour necrosis factor alpha (TNFalpha): role in suppression of apoptosis by the peroxisome proliferator Nafenopin.
Cellular and molecular biology (Noisy-le-Grand France), 2000Co-Authors: Peter R. Holden, Susan C. Hasmall, Frank J. Gonzalez, Jeffrey M. Peters, Ruth A. RobertsAbstract:Abstract The peroxisome proliferator (PPs) class of non-genotoxic rodent hepatocarcinogens induce mouse hepatocyte DNA synthesis and suppress apoptosis. This phenotype can be reproduced in vitro using exogenous tumour necrosis factor alpha (TNFalpha), suggesting a role for TNFalpha in mediating the liver growth response to PPs. In hepatocytes isolated from the peroxisome proliferator activated receptor alpha (PPARalpha) null mouse, PPs are unable to stimulate DNA synthesis or to suppress either spontaneous or TGFbeta1-induced apoptosis. However, the ability of TNFalpha to modulate hepatocyte survival and growth is unaltered, suggesting that TNFalpha acts independently or downstream of PPARalpha to mediate the growth changes associated with PPARalpha activation. Since PPARalpha is a ligand activated transcription factor, we determined if TNFalpha gene expression was altered by PP treatment during an early time window preceding PP-induced growth changes. However there was no induction of TNFalpha expression by Nafenopin over the constitutive levels noted in control cultured cells. In summary, TNFalpha acts downstream or independently of PPARalpha to mediate the suppression of apoptosis and induction of DNA synthesis by PPs. In this in vitro model, the PP Nafenopin do not appear to mediate de novo TNFalpha gene expression suggesting that the response to Nafenopin may be mediated by bioactivation or release of pre-existing TNFalpha protein from Kupffer cells.
Neil H. James - One of the best experts on this subject based on the ideXlab platform.
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Role of MAP kinase signalling pathways in the mode of action of peroxisome proliferators
Carcinogenesis, 2000Co-Authors: Sabina Cosulich, Neil H. James, Ruth A. RobertsAbstract:Peroxisome proliferators (PPs) are a class of non-genotoxic chemicals that cause rodent liver enlargement and hepatocarcinogenesis. In primary rat hepatocytes, PPs cause cell proliferation, suppression of apoptosis and peroxisome proliferation. We have investigated the role of different families of mitogen-activated protein (MAP) kinases in the mode of action of PPs. Addition of 50 microM Nafenopin to primary rat hepatocyte cultures caused weak activation of extracellular signal regulated kinases and p38 MAP kinase. However, incubation of primary hepatocytes with the p38 MAP kinase inhibitor SB203580 or the MAP kinase kinase (MEK) inhibitor PD098059 prevented the induction of DNA synthesis and the suppression of transforming growth factor beta(1)-induced apoptosis by the PP Nafenopin. In contrast, in the presence of these MAP kinase inhibitors, Nafenopin still induced palmitoyl CoA oxidation, a measure of peroxisome proliferation. We have shown previously that PPs such as Nafenopin require tumour necrosis factor alpha (TNF-alpha) to exert their effects on cellular proliferation and apoptosis. Here we show that treatment of primary rat hepatocyte cultures with Nafenopin causes an increase in bioactive TNF-alpha and that this process requires p38 MAP kinase activity.
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role for tumor necrosis factor α receptor 1 and interleukin 1 receptor in the suppression of mouse hepatocyte apoptosis by the peroxisome proliferator Nafenopin
Hepatology, 1999Co-Authors: Douglas West, Neil H. James, Sabina Cosulich, Peter R. Holden, Richard Brindle, Mark Rolfe, Ruth A. RobertsAbstract:Peroxisome proliferators (PPs) cause rodent liver enlargement and tumors. In vitro, PPs induce rat and mouse hepatocyte DNA synthesis and suppress apoptosis, a response mimicked by exogenous tumor necrosis factor alpha (TNFalpha). Here, we determine the role of TNF receptor 1 (TNFR1), TNF receptor 2 (TNFR2), and nuclear factor kappa beta (NFkappaB) in the response of mouse hepatocytes to the PP, Nafenopin. Nafenopin (50 micromol/L) induced DNA synthesis as measured by bromodeoxyuridine (BrdU) incorporation, suppressed cell death as measured by Hoechst 33258 staining, induced peroxisomal beta-oxidation as measured by cyanide insensitive palmitoyl CoA oxidation (PCO) and caused activation of nuclear factor kappa beta (NFkappaB) as determined by electrophoretic mobility gel shift assay (EMSA). The induction of DNA synthesis and the suppression of apoptosis in response to Nafenopin was abrogated completely by blocking antibodies to TNFR1 but not to TNFR2. In contrast, the induction of peroxisomal beta-oxidation by Nafenopin was not blocked by the anti-TNFR1 antibody. Next, we evaluated the response of hepatocytes to interleukin-1 (IL-1), another proinflammatory cytokine. IL-1alpha (2.5 ng/mL) and, to a lesser extent, IL-1beta (5 ng/mL), shared the ability of TNFalpha to induce DNA synthesis and suppress apoptosis. In addition, anti-IL-1 receptor, type 1/p80 (IL-1R) antibodies were able to abrogate the response to Nafenopin. IL-1alpha was still able to perturb hepatocyte growth in the presence of the anti-TNFR1 antibody suggesting that IL-1alpha acts independently rather than by elaborating TNFalpha. In summary, these data provide additional evidence for a role for hepatic cytokines in the perturbation of hepatocyte growth by PPs such as Nafenopin.
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Role for tumor necrosis factor α receptor 1 and interleukin‐1 receptor in the suppression of mouse hepatocyte apoptosis by the peroxisome proliferator Nafenopin
Hepatology (Baltimore Md.), 1999Co-Authors: Douglas A. West, Neil H. James, Sabina Cosulich, Peter R. Holden, Richard Brindle, Mark Rolfe, Ruth A. RobertsAbstract:Peroxisome proliferators (PPs) cause rodent liver enlargement and tumors. In vitro, PPs induce rat and mouse hepatocyte DNA synthesis and suppress apoptosis, a response mimicked by exogenous tumor necrosis factor alpha (TNFalpha). Here, we determine the role of TNF receptor 1 (TNFR1), TNF receptor 2 (TNFR2), and nuclear factor kappa beta (NFkappaB) in the response of mouse hepatocytes to the PP, Nafenopin. Nafenopin (50 micromol/L) induced DNA synthesis as measured by bromodeoxyuridine (BrdU) incorporation, suppressed cell death as measured by Hoechst 33258 staining, induced peroxisomal beta-oxidation as measured by cyanide insensitive palmitoyl CoA oxidation (PCO) and caused activation of nuclear factor kappa beta (NFkappaB) as determined by electrophoretic mobility gel shift assay (EMSA). The induction of DNA synthesis and the suppression of apoptosis in response to Nafenopin was abrogated completely by blocking antibodies to TNFR1 but not to TNFR2. In contrast, the induction of peroxisomal beta-oxidation by Nafenopin was not blocked by the anti-TNFR1 antibody. Next, we evaluated the response of hepatocytes to interleukin-1 (IL-1), another proinflammatory cytokine. IL-1alpha (2.5 ng/mL) and, to a lesser extent, IL-1beta (5 ng/mL), shared the ability of TNFalpha to induce DNA synthesis and suppress apoptosis. In addition, anti-IL-1 receptor, type 1/p80 (IL-1R) antibodies were able to abrogate the response to Nafenopin. IL-1alpha was still able to perturb hepatocyte growth in the presence of the anti-TNFR1 antibody suggesting that IL-1alpha acts independently rather than by elaborating TNFalpha. In summary, these data provide additional evidence for a role for hepatic cytokines in the perturbation of hepatocyte growth by PPs such as Nafenopin.
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The peroxisome proliferator Nafenopin does not suppress hepatocyte apoptosis in guinea pig liver in vivo nor in human hepatocytes in vitro.
Archives of toxicology, 1998Co-Authors: Susan C. Hasmall, Neil H. James, Anthony R. Soames, Ruth A. RobertsAbstract:In rats and mice, Nafenopin is a nongenotoxic hepatocarcinogen, which induces hepatic DNA synthesis and enzyme induction both in vivo and in hepatocyte cultures in vitro. However, humans and guinea-pigs are considered to be non-responsive to the liver growth effects of peroxisome proliferators (PPs). The ability to stimulate cell replication coupled with the ability to suppress apoptosis is thought to underpin the carcinogenicity of nongenotoxic carcinogens such as PPs. Previous studies in this laboratory have shown that in rats in vivo and in vitro Nafenopin suppressed spontaneous hepatocyte apoptosis and that induced by the physiological negative growth regulator transforming growth factors β1 (TGFβ1). In addition Nafenopin suppressed apoptosis in cultured hepatocytes from guinea-pig and hamster. The effects of PPs on apoptosis in human hepatocyte cultures is not known. To correlate these previous in vitro findings to the known species differences in hepatocarcinogenicity of PPs we have investigated the effects of Nafenopin on guinea-pig liver growth in vivo. Also, we have examined the effects of Nafenopin on apoptosis in cultures of human hepatocytes, a valuable model for human risk assessment. Nafenopin did not inhibit either spontaneous or TGFβ1 induced apoptosis in human hepatocytes in vitro. Administration of Nafenopin to guinea-pigs in vivo produced none of the changes seen previously in responsive species, such as rats and mice. There was no change in liver/body weight ratio, peroxisomal volume of hepatocytes or DNA synthesis as determined by incorporation of bromodeoxyuridine and there was no suppression of apoptosis. The lack of response to Nafenopin in guinea-pigs in vivo and human hepatocytes in vitro provides further evidence that these species may be refractory to the liver growth effects of PPs despite the ability of guinea-pigs and humans to respond to PPs by alterations in lipid metabolism. The data presented add to our overall understanding of species differences in response to the PP class of rodent nongenotoxic carcinogens.
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The non-genotoxic hepatocarcinogen Nafenopin suppresses rodent hepatocyte apoptosis induced by TGFbeta1, DNA damage and Fas.
Carcinogenesis, 1998Co-Authors: Jason H. Gill, Ruth A. Roberts, Neil H. James, Caroline DiveAbstract:The suppression of apoptosis may contribute to the carcinogenicity of the peroxisome proliferators (PPs), a class of non-genotoxic rodent hepatocarcinogens. Our previous work demonstrated that the PP Nafenopin suppressed both spontaneous and transforming growth factor beta1 (TGFbeta1)-induced hepatocyte apoptosis both in vivo and in vitro. Here, we extend these observations by demonstrating the ability of Nafenopin to suppress apoptosis induced by other major candidates for the signalling of cell death in the liver. Treatment of rat or mouse hepatocyte monolayers with TGFbeta1 or the DNA damaging drugs etoposide or hydroxyurea induced high levels of apoptosis. Western blot analysis did not support a role for either p53 or p21waf1 in etoposide-induced apoptosis in rat hepatocytes. Treatment of mouse hepatocytes with an agonistic anti-Fas antibody also resulted in an induction of high levels of apoptosis. Pre-addition and continued exposure to Nafenopin suppressed apoptosis induced by all three stimuli. Overall, our studies demonstrate that the ability of Nafenopin to protect hepatocytes from apoptosis is not restricted to species or apoptotic stimulus. It is possible, therefore, that the PPs may suppress apoptosis by acting on diverse signalling pathways. However, it seems more likely that Nafenopin suppresses hepatocyte apoptosis elicited by each death stimulus by impinging on a core apoptotic mechanism.
Kathleen M. Knights - One of the best experts on this subject based on the ideXlab platform.
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Nafenopin–, Ciprofibroyl–, and Palmitoyl–CoA Conjugation in Vitro: Kinetic and Molecular Characterization of Marmoset Liver Microsomes and Expressed MLCL1
Archives of Biochemistry and Biophysics, 2001Co-Authors: Chris Drogemuller, Sirimas Nunthasomboon, Kathleen M. KnightsAbstract:Abstract Acyl-CoA conjugation of xenobiotic carboxylic acids is catalyzed by hepatic microsomal long-chain fatty acid CoA ligases (LCL, EC 6.2.1.3). Marmosets ( Callithrix jacchus ) are considered genetically closer to humans than rodents and are used in pharmacological and toxicological studies. We have demonstrated that marmoset liver microsomes catalyze Nafenopin–, ciprofibroyl–, and palmitoyl–CoA conjugation and that only palmitoyl–CoA conjugation is significantly upregulated (1.7-fold, P C 50 values for Nafenopin–, ciprofibroyl–, and palmitoyl–CoA conjugation of 149.7, 413.4, and 3.4 μM were comparable to those reported for human liver microsomes viz, 213.7, 379.8, and 3.4 μM, respectively. Comparison with human data was enabled by the cloning of a full-length marmoset cDNA (MLCL1) that encoded a 698-amino-acid protein sharing 83% similarity with rat liver acyl-CoA synthetase (ACS1) and 93 and 90% similarity with human liver LCL1 and LCL2, respectively. MLCL1 transiently expressed in COS-7 cells activated Nafenopin ( C 50 192.9 μM), ciprofibrate ( C 50 168.7 μM), and palmitic acid ( C 50 4.5 μM) to their respective CoA conjugates. This study also demonstrated that the sigmoidal kinetics observed for Nafenopin– and ciprofibroyl–CoA conjugation were not unique to human liver microsomes but were also characteristic of marmoset liver microsomes and recombinant MLCL1. More extensive characterization of the substrate specificity of marmoset LCL isoforms will aid in determining further the suitability of marmosets as a model for human xenobiotic metabolism via acyl-CoA conjugation.
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Nafenopin-, ciprofibroyl-, and palmitoyl-CoA conjugation in vitro: kinetic and molecular characterization of marmoset liver microsomes and expressed MLCL1.
Archives of biochemistry and biophysics, 2001Co-Authors: Chris Drogemuller, Sirimas Nunthasomboon, Kathleen M. KnightsAbstract:Abstract Acyl-CoA conjugation of xenobiotic carboxylic acids is catalyzed by hepatic microsomal long-chain fatty acid CoA ligases (LCL, EC 6.2.1.3). Marmosets ( Callithrix jacchus ) are considered genetically closer to humans than rodents and are used in pharmacological and toxicological studies. We have demonstrated that marmoset liver microsomes catalyze Nafenopin–, ciprofibroyl–, and palmitoyl–CoA conjugation and that only palmitoyl–CoA conjugation is significantly upregulated (1.7-fold, P C 50 values for Nafenopin–, ciprofibroyl–, and palmitoyl–CoA conjugation of 149.7, 413.4, and 3.4 μM were comparable to those reported for human liver microsomes viz, 213.7, 379.8, and 3.4 μM, respectively. Comparison with human data was enabled by the cloning of a full-length marmoset cDNA (MLCL1) that encoded a 698-amino-acid protein sharing 83% similarity with rat liver acyl-CoA synthetase (ACS1) and 93 and 90% similarity with human liver LCL1 and LCL2, respectively. MLCL1 transiently expressed in COS-7 cells activated Nafenopin ( C 50 192.9 μM), ciprofibrate ( C 50 168.7 μM), and palmitic acid ( C 50 4.5 μM) to their respective CoA conjugates. This study also demonstrated that the sigmoidal kinetics observed for Nafenopin– and ciprofibroyl–CoA conjugation were not unique to human liver microsomes but were also characteristic of marmoset liver microsomes and recombinant MLCL1. More extensive characterization of the substrate specificity of marmoset LCL isoforms will aid in determining further the suitability of marmosets as a model for human xenobiotic metabolism via acyl-CoA conjugation.
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In vitro covalent binding of Nafenopin-CoA to human liver proteins.
Toxicology and applied pharmacology, 2000Co-Authors: Benedetta C. Sallustio, Sirimas Nunthasomboon, Chris Drogemuller, Kathleen M. KnightsAbstract:Endogenous fatty acyl–CoAs play an important role in the acylation of proteins. A number of xenobiotic carboxylic acids are able to mimic fatty acids, forming CoA conjugates and acting as substrates in pathways of lipid metabolism. In this study Nafenopin, a substrate for human hepatic fatty acid–CoA ligases, was chosen as a model compound to study xenobiotic acylation of human liver proteins. 3H-Nafenopin (± unlabeled palmitate) or 14C-palmitate (± unlabeled Nafenopin) were incubated for up to 120 min at 37°C with ATP, CoA, and homogenate protein (1 mg/ml) from four individual human livers. Nafenopin covalently bound to proteins was detectable in all human livers and increased with time. Nafenopin adduct formation was directly proportional to Nafenopin–CoA formation (r = 0.985, p 100 and 50–100 kDa, respectively. Protein acylation by palmitate was also demonstrated. Palmitate significantly inhibited Nafenopin–CoA formation by 29% but had no effect on Nafenopin–CoA-mediated protein acylation. In contrast, Nafenopin significantly inhibited protein palmitoylation by palmitoyl–CoA. This is the first study to demonstrate a direct relationship between xenobiotic–CoA formation, acylation of human liver proteins, and inhibition of endogenous palmitoylation. The ability of xenobiotics to acylate tissue proteins may have important biological consequences including perturbation of endogenous regulation of protein localization and function.
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Kinetic characteristics of rat liver peroxisomal Nafenopin-CoA ligase
Biochemical pharmacology, 1995Co-Authors: Benjamin J. Roberts, John K. Macleod, Inderjit Singh, Kathleen M. KnightsAbstract:Abstract In this study we have demonstrated that rat hepatic peroxisomes catalyse the formation of Nafenopin-CoA. The process is mediated by apparent high affinity ( K m 6.7 μ M), low capacity ( V max 0.31 nmol/mg/min) and low affinity, high capacity isoforms. Palmitic acid ( K i 1.1 μ M), r (−) ibuprofen ( K i 7.9 μ M), ciprofibrate ( K i 60.2 μ M) and clofibric acid ( K i 86.8 μ M) competitively inhibited Nafenopin-CoA formation catalysed by the apparent high affinity isoform. An antibody raised against the microsomal palmitoyl-CoA ligase inhibited the equivalent peroxisomal enzyme significantly ( P
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Differential induction of rat hepatic microsomal and peroxisomal long-chain and Nafenopin-CoA ligases by clofibric acid and di-(2-ethylhexyl)phthalate.
Xenobiotica; the fate of foreign compounds in biological systems, 1995Co-Authors: B. J. Roberts, Kathleen M. KnightsAbstract:1. Activity of rat hepatic microsomal and peroxisomal long-chain (palmitoyl) and Nafenopin-CoA ligases were studied following administration of either clofibric acid, di-(2-ethylhexyl)phthalate (DEHP) or phenobarbitone.2. Clofibric acid significantly induced the peroxisomal palmitoyl and Nafenopin-CoA ligases, whilst no induction of the equivalent enzymes was observed in the microsomal fraction.3. DEHP induced only palmitoyl-CoA formation in peroxisomes, whilst all enzymes were refractory to phenobarbitone treatment.4. The enzyme-specific patterns of induction both intra- and inter-organelle suggest that the palmitoyl and Nafenopin-CoA ligases are under different regulatory control.5. Modulation of both the rate and extent of Nafenopin-and palmitoyl-CoA formation was both agent and organelle specific.6. This study highlights the difficulty in delineating the individual roles of both fatty acyl-CoAs and xenobiotic-CoAs in peroxisome proliferation.
Patrick I. Eacho - One of the best experts on this subject based on the ideXlab platform.
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Nafenopin-induced peroxisome proliferation in vitamin A deficient rats.
Biochemical pharmacology, 1995Co-Authors: Jeffrey W. Lawrence, Patricia S. Foxworthy, David N. Perry, Charles B. Jensen, Deborah D. Giera, Vincent P. Meador, Patrick I. EachoAbstract:Abstract Induction of peroxisome proliferator responsive genes is thought to be mediated through binding of a peroxisome proliferator-activated receptor (PPAR) to specific peroxisome proliferator response elements in the upstream region of these genes. Binding of PPAR to the acyl-CoA oxidase promoter requires heterodimerization with the retinoid X receptor (RXR), and subsequent transactivation is strongest when ligands for both PPAR and RXR are present. Therefore, we hypothesized that depletion of ligand for the retinoid receptor would limit the induction of peroxisome proliferation in rats. Hepatic retinol content was reduced by more than 90% by feeding weanling rats a vitamin A deficient (VAD) diet for approximately 3 months. Nafenopin treatment for 7 days induced peroxisomal β-oxidation 18-fold in VAD rats compared with 16-fold in rats fed a vitamin A sufficient (VAS) diet. Nafenopin induced microsomal laurate hydroxylase and mitochondrial β-oxidation to comparable rates of specific activity in both VAD and VAS rats. However, the activities in VAD controls were significantly lower than in VAS controls, so the magnitude of the Nafenopin-induced increases was greater in the VAD rats. Relative liver weights were increased nearly 2-fold in both VAS and VAD rats treated with Nafenopin. Ultrastructural examination of the livers demonstrated that Nafenopin increased the number and size of peroxisomes in both VAD and VAS rats. These data demonstrate that rats with severely depleted vitamin A stores remained responsive to the peroxisome proliferator Nafenopin. Whether critical retinoid pools that supply RXR ligand (9- cis -retinoic acid) are spared in the vitamin A deficient rats remains to be determined.
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Hepatocellular DNA synthesis in rats given peroxisome proliferating agents: comparison of WY-14,643 to clofibric acid, Nafenopin and LY171883.
Carcinogenesis, 1991Co-Authors: Patrick I. Eacho, Teresa L. Lainer, Cheryl A. BrodheckerAbstract:The mitogenic effects of peroxisome proliferating agents have been implicated in their carcinogenicity. WY-14,643 stimulates an increase in hepatocellular DNA replication that persists with continued administration, but it is unclear if other peroxisome proliferators share this property. In these studies, WY-14,643 was compared to clofibric acid, Nafenopin and LY171883 given to rats in the diet for up to 30 days. DNA replication in the rat liver was quantified by immunohistochemical methods after continuous s.c. infusion of bromodeoxyuridine by osmotic minipump. During the first 7 days of treatment, WY-14,643 (0.1% in diet) and Nafenopin (0.05%) increased the percentage of bromodeoxyuridine-labeled hepatocytes to greater than 50%, from 3% in controls. Clofibric acid (0.5%) and LY171883 (0.3%) increased the labeling to approximately 33%. The replicative response to each of the compounds was localized primarily to the periportal region of the liver lobule. The time-course of replication induced by clofibric acid and WY-14,64.3 was examined over 3 day intervals. The peak of replication in response to clofibric acid occurred during days 4-6, whereas the effect of WY-14,643 peaked during days 1-3 and was much greater than clofibric acid. The replicative response to WY-14,643 persisted through 30 days at dietary concentrations of 0.1 and 0.005%. Nafenopin, LY171883 and clofibric acid were without effect on DNA replication on days 28-30 even though the hepatomegaly and induction of peroxisomal beta-oxidation persisted. Thus, under the conditions of these experiments, the persistent replicative effect through 30 days was unique to WY-14,643. Although sustained replication in the general population of hepatocytes may be involved in the carcinogenesis of WY-14,643, it does not appear to be a factor in the hepatocarcinogenesis of the other peroxisome proliferators.
R.j. Price - One of the best experts on this subject based on the ideXlab platform.
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Comparison of the hepatic effects of Nafenopin and WY-14,643 on peroxisome proliferation and cell replication in the rat and Syrian hamster.
Environmental Health Perspectives, 1993Co-Authors: Brian G. Lake, John G. Evans, Morag E. Cunninghame, R.j. PriceAbstract:Male Sprague-Dawley rats were fed control diet or diet containing 0.05% Nafenopin (NAF) or 0.025% WY-14,643 (WY) and male Syrian hamsters were fed control diet or diet containing 0.25% NAF or 0.025...
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Comparison of the effects of Nafenopin on hepatic peroxisome proliferation and replicative DNA synthesis in the rat and Syrian hamster.
Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association, 1992Co-Authors: R.j. Price, John G. Evans, Brian G. LakeAbstract:Male Sprague-Dawley rats were fed control or 0.1% Nafenopin diet and male Syrian hamsters were fed control or 0.25% Nafenopin diet for periods of 7 and 54 days. Nafenopin treatment produced a sustained increase in liver weight and induction of hepatic peroxisomal and microsomal fatty acid-oxidizing enzyme activities, with a greater effect being observed in the rat. Replicative DNA synthesis was studied by implanting osmotic pumps containing [3H]thymidine during study days 0–7 and 47–54. Cell replication, determined either as the hepatocyte labelling index or by incorporation of radioactivity into liver whole homogenate DNA, was increased in rats given Nafenopin for 7 and 54 days. In contrast to the rat, no significant effect on replicative DNA synthesis was observed in the Syrian hamster. These results provide further evidence for species differences in hepatic peroxisome proliferation, with the Syrian hamster being less responsive than the rat. Furthermore, while peroxisome proliferators produce hyperplasia in rat and mouse liver, these data suggest that they may not have any marked effect on hepatic replicative DNA synthesis in the Syrian hamster.