RESUMEN
The profile of liver acyl-CoAs induced by dietary fats of variable compositions or by xenobiotic hypolipidemic amphipathic carboxylates was evaluated in vivo using a novel electrospray ionization tandem mass spectrometry methodology of high resolution, sensitivity, and reliability. The composition of liver fatty acyl-CoAs was found to reflect the composition of dietary fat. Treatment with hypolipidemic carboxylates resulted in liver dominant abundance of their respective acyl-CoAs accompanied by an increase in liver fatty acyl-CoAs. Cellular effects exerted by dietary fatty acids and/or xenobiotic carboxylic drugs may be transduced in vivo by their respective acyl-CoAs.
Asunto(s)
Acilcoenzima A/análisis , Grasas de la Dieta/farmacología , Hígado/química , Hígado/efectos de los fármacos , Xenobióticos/farmacología , Acilcoenzima A/metabolismo , Animales , Bezafibrato/farmacología , Dieta , Hipolipemiantes/farmacología , Masculino , Nafenopina/farmacología , Ácidos Palmíticos/farmacología , Ratas , Sensibilidad y Especificidad , Espectrometría de Masa por Ionización de Electrospray/métodosRESUMEN
Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the superfamily of nuclear receptors. It binds and is activated by natural polyunsaturated fatty acids, eicosanoids, synthetic thiazolidinediones and related analogues. Biological effects exerted by PPARgamma ligands are mostly concerned with differentiation processes, sensitization to insulin and atherogenesis, and are paradigmatically ascribed to PPARgamma transactivation of PPARgamma-responsive genes. The PPARgamma paradigm and its consequences in humans are analyzed here in terms of the tissue specificity of PPARgamma, loss and gain of function mutants of PPARgamma, PPARgamma-responsive genes and clinical effects of PPARgamma ligands. Differentiation, as well as some of the atherogenic effects induced by PPARgamma ligands, does conform to the PPARgamma paradigm. However, sensitization to insulin as well as some of the antiatherogenic effects of PPARgamma ligands is not accounted for by PPARgamma activation, thus calling for an alternative target for insulin sensitizers.
Asunto(s)
Receptores Citoplasmáticos y Nucleares/fisiología , Factores de Transcripción/fisiología , Animales , Arteriosclerosis/etiología , Diferenciación Celular , Citocinas/fisiología , Células Espumosas/fisiología , Humanos , Insulina/farmacología , Músculo Liso Vascular/citología , Especificidad de Órganos , Inhibidor 1 de Activador Plasminogénico/fisiologíaRESUMEN
Hepatocyte nuclear factor-4alpha (HNF-4alpha) modulates the expression of liver-specific genes that control the production (e.g. apolipoprotein [apo] A-I and apo B) and clearance (e.g. apo C-III) of plasma lipoproteins. We reported that the CoA thioesters of amphipathic carboxylic hypolipidemic drugs (e.g. clofibric acid analogues currently used for treating hyperlipidemia in humans and substituted long-chain dicarboxylic acids) were formed in vivo, bound to HNF-4alpha, inhibited its transcriptional activity, and suppressed the expression of HNF-4alpha-responsive genes. Hypolipidemic PPARalpha (peroxisome proliferator-activated receptor alpha) activators that were not endogenously thioesterified into their respective acyl-CoAs were shown to be effective in rats but not in humans, implying that the hypolipidemic activity transduced by PPARalpha in rats was PPARalpha-independent in humans. The suppressed acyl-CoA synthase of PPARalpha knockout mice left unresolved the contribution made by the acyl-CoA/HNF-4alpha pathway to the hypolipidemic effect of PPARalpha agonists in rodents. Hence, suppression of HNF-4alpha activity by the CoA thioesters of hypolipidemic "peroxisome proliferators" may account for their hypolipidemic activity independently of PPARalpha activation by their respective free carboxylates. The hypolipidemic activity of peroxisome proliferators is mediated in rats and humans by the PPARalpha and HNF-4alpha pathways, respectively.
Asunto(s)
Proteínas de Unión al ADN , Hipolipemiantes/metabolismo , Hígado/metabolismo , Proliferadores de Peroxisomas/metabolismo , Fosfoproteínas/metabolismo , Factores de Transcripción/metabolismo , Animales , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice , Células COS , Factor Nuclear 4 del Hepatocito , Humanos , Hipolipemiantes/farmacología , Hígado/citología , Hígado/efectos de los fármacos , Ácidos Palmíticos/farmacología , Proliferadores de Peroxisomas/farmacología , Fosfoproteínas/antagonistas & inhibidores , Ratas , Receptores Citoplasmáticos y Nucleares/metabolismo , Factores de Transcripción/antagonistas & inhibidores , Transcripción GenéticaRESUMEN
Adipose tissue lipolysis and fatty acid reesterification by liver and adipose tissue were investigated in rats fasted for 15 h under basal and calorigenic conditions. The fatty acid flux initiated by adipose fat lipolysis in the fasted rat is mostly futile and is characterized by reesterification of 57% of lipolyzed free fatty acid (FFA) back into adipose triglycerides (TG). About two-thirds of FFA reesterification are carried out before FFA release into plasma, whereas the rest consists of plasma FFA extracted by adipose tissue. Thirty-six percent of the fasting lipolytic flux is accounted for by oxidation of plasma FFA, whereas only a minor fraction is channeled into hepatic very low density lipoprotein-triglycerides (VLDL-TG). Total body calorigenesis induced by thyroid hormone treatment and liver-specific calorigenesis induced by treatment with beta, beta'-tetramethylhexadecanedioic acid (Medica 16) are characterized by a 1.7- and 1.3-fold increase in FFA oxidation, respectively, maintained by a 1.5-fold increase in adipose fat lipolysis. Hepatic reesterification of plasma FFA into VLDL-TG is negligible under both calorigenic conditions. Hence, total body fatty acid metabolism is regulated by adipose tissue as both source and sink. The futile nature of fatty acid cycling allows for its fine tuning in response to metabolic demands.
Asunto(s)
Ayuno/fisiología , Ácidos Grasos/metabolismo , Tejido Adiposo/metabolismo , Animales , Regulación de la Temperatura Corporal/fisiología , Esterificación , Hipolipemiantes/farmacología , Lipólisis/fisiología , Hígado/metabolismo , Hígado/fisiología , Masculino , Oxidación-Reducción , Ácidos Palmíticos/farmacología , Ratas , Ratas Endogámicas , Hormonas Tiroideas/farmacología , Triglicéridos/metabolismoRESUMEN
Calcium-dependent uncoupling of liver mitochondrial oxidative phosphorylation by a non-metabolizable long chain fatty acyl analogue was compared with uncoupling induced by in vivo thyroid hormone treatment. beta,beta'-Methyl-substituted hexadecane alpha, omega-dioic acid (Medica 16) is reported here to induce a saturable 20-30% decrease in liver mitochondrial DeltaPsi, DeltapH and protonmotive force which proceeds in the presence of added Ca(2+) to cyclosporin A-sensitive mitochondrial permeabilization. Ca(2+)-dependent uncoupling by Medica 16 was accompanied by atractylate-enhanced, bongkrekic-inhibited activation of mitochondrial Ca(2+) efflux. The direct mitochondrial effect exerted in vitro by Medica 16 is similar to that induced by in vivo thyroid hormone treatment. Hence, the thyromimetic protonophoric activity of Medica 16 and the uncoupling activity of TH converge onto components of the mitochondrial permeabilization transition pore.
Asunto(s)
Hipolipemiantes/farmacología , Canales Iónicos , Mitocondrias Hepáticas/metabolismo , Ácidos Palmíticos/farmacología , Animales , Hipertiroidismo/metabolismo , Hipotiroidismo/metabolismo , Masculino , Proteínas de la Membrana/metabolismo , Metimazol , Mitocondrias Hepáticas/efectos de los fármacos , Proteínas de Transporte de Membrana Mitocondrial , Poro de Transición de la Permeabilidad Mitocondrial , Fuerza Protón-Motriz , Ratas , Triyodotironina , DesacopladoresRESUMEN
The JCR:LA-cp rat develops an extreme obese/insulin-resistant syndrome such that by 12 weeks of age, there is no longer any insulin-mediated glucose turnover. At 4 weeks of age, obese and lean rats have essentially identical basal and insulin-mediated glucose uptake in skeletal muscle. By 8 weeks of age, however, the obese rats no longer exhibit such intake. Plasma insulin concentrations in the normal fed state show only small increases up to 4 weeks, with a rapid rise to a marked hyperinsulinemia thereafter, with an age at half-development of 5.5 weeks. Plasma triacylglycerol concentrations in fed obese rats are elevated at 3 weeks and rise rapidly thereafter. The triacylglycerol content of skeletal muscle is significantly elevated in the obese rats at 4 weeks of age. Histological examination of Oil Red O-stained muscle tissue and transmission electron microscopy shows the presence of intracellular lipid droplets. Treatment with the potent triacylglycerol-lowering agent MEDICA 16 (beta,beta'-tetramethylhexadecanedioic acid) from 6 weeks of age reduces plasma lipids markedly, but it reduces body weight and insulin resistance only modestly. In contrast, treatment with MEDICA 16 from the time of weaning at 3 weeks of age results in the normalization of food intake and body weight to over 8 weeks of age. The development of hyperinsulinemia is also delayed until 8.5 weeks of age, and insulin levels remain strongly reduced. Plasma triacylglycerol concentrations remain at the same level as in lean rats, and neither an elevated muscle triacylglycerol content nor intracellular lipid droplets are found at 4 weeks of age. The results indicate that insulin resistance develops in the young animals and is not directly due to a genetically determined defect in insulin metabolism. The mechanism of induction instead appears to be related to an exaggerated triacylglycerol metabolism.
Asunto(s)
Hipertrigliceridemia/tratamiento farmacológico , Hipolipemiantes/farmacología , Resistencia a la Insulina/genética , Obesidad/genética , Ácidos Palmíticos/farmacología , Triglicéridos/fisiología , Animales , Desoxiglucosa/farmacocinética , Hipertrigliceridemia/genética , Insulina/sangre , Tasa de Depuración Metabólica , Microscopía Electrónica , Músculos/metabolismo , Músculos/ultraestructura , Ratas , Ratas Endogámicas , Síndrome , Distribución Tisular , Triglicéridos/sangreRESUMEN
Dietary fatty acids specifically modulate the onset and progression of various diseases, including cancer, atherogenesis, hyperlipidaemia, insulin resistances and hypertension, as well as blood coagulability and fibrinolytic defects; their effects depend on their chain length and degree of saturation. Hepatocyte nuclear factor-4alpha (HNF-4alpha) is an orphan transcription factor of the superfamily of nuclear receptors and controls the expression of genes that govern the pathogenesis and course of some of these diseases. Here we show that long-chain fatty acids directly modulate the transcriptional activity of HNF-4alpha by binding as their acyl-CoA thioesters to the ligand-binding domain of HNF-4alpha. This binding may shift the oligomeric-dimeric equilibrium of HNF-4alpha or may modulate the affinity of HNF-4alpha for its cognate promoter element, resulting in either activation or inhibition of HNF-4alpha transcriptional activity as a function of chain length and the degree of saturation of the fatty acyl-CoA ligands. In addition to their roles as substrates to yield energy, as an energy store, or as constituents of membrane phospholipids, dietary fatty acids may affect the course of a disease by modulating the expression of HNF-4alpha-controlled genes.
Asunto(s)
Acilcoenzima A/metabolismo , Grasas de la Dieta/metabolismo , Fosfoproteínas/metabolismo , Proteínas Represoras , Proteínas de Saccharomyces cerevisiae , Factores de Transcripción/metabolismo , Animales , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice , Células COS , Coenzima A Ligasas/genética , Coenzima A Ligasas/metabolismo , ADN/metabolismo , Proteínas de Unión al ADN/metabolismo , Elementos de Facilitación Genéticos , Escherichia coli , Ésteres/metabolismo , Ácidos Grasos/metabolismo , Ácidos Grasos no Esterificados/metabolismo , Factor Nuclear 4 del Hepatocito , Humanos , Ligandos , Palmitoil-CoA Hidrolasa/genética , Palmitoil-CoA Hidrolasa/metabolismo , Fosfoproteínas/agonistas , Fosfoproteínas/antagonistas & inhibidores , Ratas , Proteínas Recombinantes de Fusión/metabolismo , Factores de Transcripción/agonistas , Factores de Transcripción/antagonistas & inhibidores , Transcripción Genética , TransfecciónRESUMEN
Mitochondria uncoupling by fatty acids in vivo is still questionable, being confounded by their dual role as substrates for oxidation and as putative genuine uncouplers of oxidative phosphorylation. To dissociate between substrate and the uncoupling activity of fatty acids in oxidative phosphorylation, the uncoupling effect was studied here using a nonmetabolizable long chain fatty acyl analogue. beta,beta'-Methyl-substituted hexadecane alpha,omega-dioic acid (MEDICA 16) is reported here to induce in freshly isolated liver cells a saturable oligomycin-insensitive decrease in mitochondrial proton motive force with a concomitant increase in cellular respiration. Similarly, MEDICA 16 induced a saturable decrease in membrane potential, proton gradient, and proton motive force in isolated liver and heart mitochondria accompanied by an increase in mitochondrial respiration. Uncoupling by MEDICA 16 in isolated mitochondria was partially suppressed by added atractyloside. Hence, fatty acids may act as genuine uncouplers of cellular oxidative phosphorylation by interacting with specific mitochondrial proteins, including the adenine nucleotide translocase.
Asunto(s)
Mitocondrias Hepáticas/efectos de los fármacos , Ácidos Palmíticos/farmacología , Desacopladores/farmacología , Animales , Atractilósido/farmacología , Respiración de la Célula/efectos de los fármacos , Células Cultivadas , Ácidos Grasos/farmacología , Citometría de Flujo , Concentración de Iones de Hidrógeno , Potenciales de la Membrana/efectos de los fármacos , Mitocondrias Cardíacas/efectos de los fármacos , Translocasas Mitocondriales de ADP y ATP/metabolismo , Oligomicinas/farmacología , Fosforilación Oxidativa/efectos de los fármacos , Oxígeno/metabolismo , Ácido Palmítico/farmacología , RatasRESUMEN
Amphipathic carboxylates collectively defined as peroxisome proliferators (PP) induce in rodents a pleiotropic effect, mediated by the peroxisome proliferator-activated receptor alpha (PPAR alpha). Treatment with PP results in rodents in hypolipidemia, peroxisome proliferation and liver hypertrophy and hyperplasia leading to non-genotoxic hepatocarcinogenesis. In contrast to rodents, the hypolipidemic effect exerted by PP in humans is not accompanied by peroxisome proliferation nor by induction of peroxisomal beta-oxidation or other activities induced by PP in rodents. Non-responsiveness in humans may be ascribed to a missing liver component in the PPAR alpha transduction pathway specifically involved with transcriptional modulation of chromosomal PPAR alpha responsive genes. Hence, biological effects exerted by PP in the human liver are likely to be mediated by a transduction pathway independent of PPAR alpha.
Asunto(s)
Hígado/efectos de los fármacos , Proliferadores de Peroxisomas/toxicidad , Receptores Citoplasmáticos y Nucleares/fisiología , Factores de Transcripción/fisiología , Animales , Humanos , Hipolipemiantes/farmacología , Proliferadores de Peroxisomas/farmacología , Ratas , Especificidad de la EspecieRESUMEN
Beta,beta'-methyl-substituted hexadecanedioic acid (MEDICA 16) consists of a nonmetabolizable long-chain fatty acid designed to probe the effect exerted by fatty acids on insulin sensitivity. The effect of MEDICA 16 was evaluated in insulin-resistant Zucker (fa/fa) rats in terms of liver, muscle, and adipose tissue response to clamped euglycemic hyperinsulinemia in vivo. Nontreated Zucker rats were insulin resistant, maintaining basal rates of total-body glucose disposal, glucose production in liver, free fatty acid (FFA) flux into plasma, and FFA reesterification in adipose tissue, irrespective of the insulin levels induced. MEDICA 16 treatment resulted in an insulin-induced decrease in hepatic glucose production, together with an insulin-induced increase in total-body glucose disposal. Intracellular reesterification of lipolysed FFA in adipose tissue was specifically activated by MEDICA 16, resulting in a pronounced decrease in FFA release, with a concomitant decrease in plasma FFA. In conclusion, MEDICA 16 treatment results in the sensitization of liver, muscle, and adipose tissue to insulin in an animal model for obesity-induced insulin resistance.
Asunto(s)
Hipolipemiantes/farmacología , Resistencia a la Insulina , Insulina/farmacología , Obesidad/metabolismo , Ácidos Palmíticos/farmacología , Tejido Adiposo/efectos de los fármacos , Tejido Adiposo/metabolismo , Animales , Glucemia/metabolismo , Colesterol/sangre , Ácidos Grasos no Esterificados/sangre , Glucosa/biosíntesis , Técnica de Clampeo de la Glucosa , Insulina/sangre , Cinética , Hígado/efectos de los fármacos , Hígado/metabolismo , Músculos/efectos de los fármacos , Músculos/metabolismo , Ácido Palmítico/sangre , Ratas , Ratas Zucker , Triglicéridos/sangreAsunto(s)
Apolipoproteínas C/genética , Proteínas de Unión al ADN , Regulación Enzimológica de la Expresión Génica/efectos de los fármacos , Hipolipemiantes/farmacología , Microcuerpos/efectos de los fármacos , Animales , Apolipoproteína C-III , Bezafibrato/farmacología , Núcleo Celular/metabolismo , Factor Nuclear 4 del Hepatocito , Ácidos Palmíticos/farmacología , Fosfoproteínas/fisiología , Ratas , Factores de Transcripción/fisiología , Transcripción Genética/efectos de los fármacosRESUMEN
Peroxisome proliferators induce thyroid-hormone-dependent liver activities, e.g. 'malic' enzyme, mitochondrial glycerol-3-phosphate dehydrogenase, glucose-6-phosphate dehydrogenase, S14[Hertz, Aurbach, Hashimoto and Bar-Tana (1991) Biochem. J. 274, 745-751]. Here we report that the thyromimetic effect of peroxisome proliferators with respect to 'malic' enzyme result from transcriptional activation of the 'malic' enzyme gene, mediated by binding of the peroxisome proliferator activated receptor (PPAR alpha)/retinoid X receptor (RXR alpha) heterodimer to a 5'-flanking enhancer of the 'malic' enzyme promoter. The enhancer involved is distinct from the thyroid hormone response element of the 'malic' enzyme promoter and is partly homologous with that which mediates transcriptional activation of peroxisomal acyl-CoA oxidase by peroxisome proliferators. Hence transcriptional activation of thyroid-hormone-dependent liver genes by xenobiotic or endogenous amphipathic carboxylates collectively defined as peroxisome proliferators is mediated by a transduction pathway similar to that involved in transcriptional activation of peroxisomal beta-oxidative genes and distinct from that which mediates thyroid hormone action.
Asunto(s)
Regulación Enzimológica de la Expresión Génica , Malato Deshidrogenasa/genética , Péptidos/farmacología , Receptores Citoplasmáticos y Nucleares/metabolismo , Factores de Transcripción/metabolismo , Animales , Huella de ADN , Activación Enzimática , Hígado/efectos de los fármacos , Hígado/enzimología , Malato Deshidrogenasa/metabolismo , Masculino , Regiones Promotoras Genéticas , RatasRESUMEN
Xenobiotic amphipathic carboxylates, known collectively as hypolipidemic peroxisome proliferators (e.g., aryloxyalkanoic acids), or native long-chain fatty acids induce liver peroxisome proliferation and other biological activities. This broad spectrum of effects results from modulation of transcription of specific genes mediated by binding of peroxisome-proliferators-activated receptors (PPAR) to respective sequence-specific promoter elements (PPRE). The broad specificity and relatively low potency of reported hypolipidemic peroxisome proliferators prompted us to search for specific highly potent peroxisome proliferators. Here we report that stable prostacyclin analogues may act in such a manner. mPPAR alpha-mediated expression of a reporter gene linked to the peroxisomal rat acyl-CoA oxidase promoter was dose-dependently induced by carbaprostacyclin and iloprost. The ED50 for carbaprostacyclin was 25 nM, and carbaprostacyclin was therefore 25-fold and 200-fold more effective than the most potent xenobiotic (5,18,11,14-eicosatetraynoic acid) and native (arachidonic acid) inducers, respectively. Induction was further increased by cotransfecting the cells with mPPAR alpha and an expression vector for retinoic acid-X-receptor. PPAR-mediated activation of gene expression by prostacyclin analogues was specific for PPAR and was not observed using other members of the superfamily. No activation of gene expression was induced by other prostaglandins or leukotrienes at concentrations 100-fold higher than those of the prostacyclin analogues. Induction of gene expression by prostacyclin analogues was inhibited in cells transfected with the long-chain-acyl-CoA synthase, indicating that the acidic form of prostacyclin, rather than the respective CoA derivative or a metabolite derived thereof, serves as the activator of the PPAR/PPRE transduction pathway. Hence, PPAR-mediated modulation of gene transcription by prostacyclins may form the basis for their novel role as regulators of gene expression. Xenobiotic hypolipidemic peroxisome proliferators and native long-chain fatty acids seem to exploit the PPAR/PPRE transduction pathway used by prostacyclin.
Asunto(s)
Epoprostenol/análogos & derivados , Regulación de la Expresión Génica/efectos de los fármacos , Receptores Citoplasmáticos y Nucleares/metabolismo , Factores de Transcripción/metabolismo , Animales , Línea Celular , Epoprostenol/farmacología , Genes Reporteros , Hígado/efectos de los fármacos , Hígado/metabolismo , Microcuerpos/efectos de los fármacos , Ratas , Receptores Citoplasmáticos y Nucleares/efectos de los fármacos , Receptores de Ácido Retinoico/metabolismo , Receptores X Retinoide , Transducción de Señal , Factores de Transcripción/efectos de los fármacos , TransfecciónRESUMEN
Activation of gene expression by hypolipidemic peroxisome proliferators (e.g. native and substituted long chain fatty acids, aryloxyalkanoic fibrate drugs) is accompanied by transcriptional suppression of liver transferrin gene in treated animals or human hepatoma cell line. Transcriptional suppression of liver transferrin by hypolipidemic peroxisome proliferators results from (a) displacement of hepatic nuclear factor (HNF)-4 from the transferrin promoter by nonproductive binding of the peroxisome proliferator-activated receptor-retinoic acid X receptor heterodimer to the (-76/-52) PRI promoter element of the human transferrin gene and (b) suppression of liver HNF-4 gene expression by hypolipidemic peroxisome proliferators with a concomitant decrease in its availability for binding to the transferrin PRI promoter element. HNF-4 gene suppression and its displacement from the transferrin promoter result in eliminating HNF-4-enhanced transcription of transferrin. Liver transferrin suppression by hypolipidemic peroxisome proliferators may result in reduced iron availability as well as modulation of transferrin-induced differentiation processes. Transcriptional suppression of HNF-4-enhanced liver genes (e.g. apolipoprotein C-III, transferrin) may complement the pleiotropic biological effect exerted by hypolipidemic peroxisome proliferators.
Asunto(s)
Hipolipemiantes/farmacología , Microcuerpos/efectos de los fármacos , Transcripción Genética/efectos de los fármacos , Transferrina/genética , Animales , Secuencia de Bases , Línea Celular , Cloranfenicol O-Acetiltransferasa/genética , Humanos , Hígado/efectos de los fármacos , Hígado/metabolismo , Masculino , Datos de Secuencia Molecular , Oligodesoxirribonucleótidos , Regiones Promotoras Genéticas , ARN Mensajero/genética , ARN Mensajero/metabolismo , Ratas , Receptores Citoplasmáticos y Nucleares/metabolismo , Receptores de Ácido Retinoico/metabolismo , Receptores X Retinoide , Factores de Transcripción/metabolismo , Transferrina/metabolismo , Células Tumorales CultivadasRESUMEN
Nonmetabolizable fatty acids are shown here to induce adipose conversion of 3T3-L1 preadipocytes as well as to activate transcription of a reporter plasmid promoted by a peroxisome proliferators response element. This dual activity was also observed using the peroxisome proliferator bezafibrate or the differentiation inducer isobutyl methylxanthine. The data suggest a role for a peroxisome proliferators activated receptor (PPAR) in adipose conversion induced by fatty acids, isobutyl methylxanthine, or xenobiotic amphipathic carboxylates.
Asunto(s)
Tejido Adiposo/efectos de los fármacos , Hipolipemiantes/farmacología , Microcuerpos/efectos de los fármacos , Receptores Citoplasmáticos y Nucleares/efectos de los fármacos , Factores de Transcripción/efectos de los fármacos , 1-Metil-3-Isobutilxantina/farmacología , Células 3T3 , Animales , Bezafibrato/farmacología , Diferenciación Celular/efectos de los fármacos , Cloranfenicol O-Acetiltransferasa/análisis , Cloranfenicol O-Acetiltransferasa/genética , Hipoglucemiantes/farmacología , Ratones , Palmitatos/farmacología , Ácidos Palmíticos/farmacología , Plásmidos , Receptores Citoplasmáticos y Nucleares/genética , Factores de Transcripción/genética , Transcripción Genética/efectos de los fármacos , TransfecciónRESUMEN
Thyroid hormone treatment in vivo results in activation of mitochondrial Ca2+ efflux and temperature-dependent enhanced swelling of Ca(2+)-loaded rat liver mitochondria. Thyroid hormone-induced swelling was effectively prevented in the presence of excess EGTA or cyclosporin A. Thyroid hormone treatment similarly resulted in a dramatic decrease in mitochondrial membrane potential (80%), proton gradient (45%), and proton motive force (69%) measured in Ca(2+)-loaded mitochondria. All three parameters were essentially restored to euthyroid values in the presence of excess EGTA or cyclosporin A. Mitochondrial energy-linked transhydrogenase activity measured in the presence of Ca2+ was 33% increased and 38% decreased in hypothyroid and L-T3-treated hypothyroid rats, respectively, compared to that in euthyroid rats. Hence, in vivo thyroid hormone treatment may induce mitochondrial permeability transition mediated by the cyclosporin A-sensitive permeability transition pore.
Asunto(s)
Mitocondrias Hepáticas/efectos de los fármacos , Mitocondrias Hepáticas/metabolismo , Hormonas Tiroideas/farmacología , Animales , Calcio/metabolismo , Ciclosporina/farmacología , Ácido Egtácico/farmacología , Metabolismo Energético , Hipotiroidismo/metabolismo , Masculino , NADP Transhidrogenasas/metabolismo , Permeabilidad , Ratas , Valores de Referencia , Temperatura , Triyodotironina/farmacologíaRESUMEN
Atherosclerosis-prone, insulin-resistant JCR:LA-cp male rats were treated from 6 weeks to 39 weeks of age with beta,beta'-tetramethylhexadecanedioic acid (MEDICA 16). Body weights were reduced (13%, P < .001) at 36 weeks without any accompanying decrease in food consumption. The treatment did not cause any significant change in plasma glucose or fasting insulin concentrations. There was a significant decrease in the extreme hyperplasia of the islets of Langerhans (38%, P < .05). The marked VLDL hypertriglyceridemia was decreased by 70% (P < .001), with an accompanying significant reduction in cholesterol concentrations. The severity of raised atherosclerotic lesions on the aortic arch was very markedly reduced (P < .01) in treated rats. This was accompanied by a reduction (P < .01) in the incidence of ischemic myocardial lesions. We conclude that long-term (33 weeks) MEDICA 16 treatment of an animal model for the obesity/insulin-resistant/hyperlipidemic syndrome not only markedly improved lipid metabolism, but also inhibited the development of advanced cardiovascular disease.
Asunto(s)
Arteriosclerosis/prevención & control , Cardiomiopatías/prevención & control , Ácidos Palmíticos/uso terapéutico , Animales , Aorta/patología , Arteriosclerosis/patología , Peso Corporal , Cardiomiopatías/patología , Endotelio Vascular/patología , Lípidos/sangre , Macrófagos/patología , Masculino , Microscopía Electrónica de Rastreo , Páncreas/patología , Ratas , Ratas MutantesRESUMEN
The hypolipidemic effect exerted by beta,beta'-tetramethyl-hexadecanedioic acid (Medica 16) is accounted for by enhanced catabolism of plasma triglyceride-rich lipoproteins due to a decrease in plasma apolipoprotein C-III (Frenkel, B., Mayorek, N., Hertz, R., and Bar-Tana, J. (1988) J. Biol. Chem. 263, 8491-8497; Frenkel, B., Bishara-Shieban, J., and Bar-Tana, J. (1994) Biochem. J. 298, 409-414). Decrease in apolipoprotein C-III exerted by peroxisome proliferators/hypolipidemic amphipathic carboxylates (e.g. Medica 16, fibrate drugs) is shown here to result from suppression of apolipoprotein C-III gene expression. Transcriptional suppression of apolipoprotein C-III is due to transcriptional suppression of hepatic nuclear factor (HNF)-4 as well as displacement of HNF-4 from the apolipoprotein C-III promoter. HNF-4 displacement exerted by peroxisome proliferators/hypolipidemic amphipathic carboxylates is mediated by the peroxisome proliferators activated receptor (PPAR). Transcriptional suppression of HNF-4-enhanced genes (e.g. apolipoprotein C-III) along with transcriptional activation of peroxisomal and other genes by hypolipidemic drugs may account for their broad spectrum pharmacological effect.
Asunto(s)
Apolipoproteínas C/antagonistas & inhibidores , Proteínas de Unión al ADN , Hipolipemiantes/farmacología , Microcuerpos/efectos de los fármacos , Ácidos Palmíticos/farmacología , Fosfoproteínas , Animales , Apolipoproteína C-III , Apolipoproteínas C/sangre , Apolipoproteínas C/genética , Secuencia de Bases , Factores de Transcripción Básicos con Cremalleras de Leucinas y Motivos Hélice-Asa-Hélice , Línea Celular , Factor Nuclear 4 del Hepatocito , Humanos , Masculino , Datos de Secuencia Molecular , Oligodesoxirribonucleótidos , ARN Mensajero/metabolismo , Ratas , Factores de Transcripción/genética , Transcripción GenéticaRESUMEN
Amphiphilic carboxylates acting as peroxisome proliferators and hypolipidemic drugs induce enzymes of peroxisomal lipid beta-oxidation, certain drug-metabolizing enzymes in the liver, and a number of additional proteins. The peroxisome proliferators represent a well-established class of non-genotoxic hepatocarcinogens. In this study we characterized the hepatic elimination of the peroxisome proliferator nafenopin. In the rat in vivo, 1 hr after intravenous administration of [3H]nafenopin, approx. 40% of injected radioactivity was recovered in bile. HPLC analysis of bile samples revealed that only about 10% of the radioactivity recovered in bile was associated with non-metabolized nafenopin and approx. 90% with more polar metabolites. One of the main metabolites formed in the liver and excreted into bile was identified as nafenopin glucuronide by beta-glucuronidase-catalysed reconversion to nafenopin. In mutant rats deficient in the canalicular transport of leukotriene C4 and related amphiphilic anion conjugates, recovery of [3H]nafenopin-derived radioactivity in bile was reduced to 4% of the injected dose. Although nafenopin glucuronide could not be detected in bile, it was a major metabolite in the liver from these mutant rats. Using membrane vesicles enriched in bile canalicular membranes from normal rats, transport of nafenopin glucuronide was shown to be a primary-active ATP-dependent process which was inhibited by leukotriene C4 and S-dinitrophenyl glutathione with IC50 values of 0.2 and 12 microM, respectively. ATP-dependent transport was not detectable for non-conjugated nafenopin. In canalicular membrane vesicles prepared from the mutant rats, the rate of ATP-dependent transport of nafenopin glucuronide was less than 10% of the transport observed in vesicles from normal rats. These data indicate that conjugation and subsequent transport by the ATP-dependent export carrier for leukotriene C4 and related conjugates is a major pathway for the elimination of nafenopin and structurally-related peroxisome proliferators.
Asunto(s)
Canalículos Biliares/metabolismo , Hígado/metabolismo , Nafenopina/metabolismo , Adenosina Trifosfato/metabolismo , Animales , Bilis/metabolismo , Canalículos Biliares/ultraestructura , Transporte Biológico , Glucuronatos/metabolismo , Masculino , Mutación , Ratas , Ratas Wistar , TritioRESUMEN
Most peroxisomal proliferators consist of a carboxylic group attached to a hydrophobic backbone yielding an amphipathic carboxylate molecule. The respective CoA derivatives of peroxisomal proliferators, formed by ATP-dependent CoA thioesterification catalyzed by long-chain-acyl-CoA synthase, have been repeatedly considered as the immediate inducers of peroxisome and other genes. In this study, the putative requirement for prior CoA thioesterification of peroxisomal proliferators was evaluated by analyzing the induced expression of a reporter plasmid promoted by the peroxisomal acyl-CoA-oxidase promoter in cells transiently cotransfected with expression vectors for the peroxisome-proliferator-activated receptor and the long-chain-acyl-CoA synthase. Transcriptional activation of peroxisomal acyl-CoA oxidase by peroxisomal proliferators was inhibited in the presence of transfected functional acyl-CoA synthase. The inhibitory effect was negatively correlated with the capacity of the acyl-CoA synthase to catalyze CoA thioesterification of the respective proliferator. Hence, the immediate inducer is the peroxisomal proliferator free acid rather than the respective CoA derivative or a metabolite derived from the peroxisomal-proliferator-CoA intermediate.