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2.
Biochemistry ; 40(41): 12243-53, 2001 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-11591143

RESUMO

Overexpression of human apolipoprotein A-II (apo A-II) in mice induced postprandial hypertriglyceridemia and marked reduction in plasma HDL concentration and particle size [Boisfer et al. (1999) J. Biol. Chem. 274, 11564-11572]. We presently compared lipoprotein metabolism in three transgenic lines displaying plasma concentrations of human apo A-II ranging from normal to 4 times higher, under ad libitum feeding and after an overnight fast. Fasting dramatically decreased VLDL and lowered circulating human apo A-II in transgenic mice; conversely, plasma HDL levels increased in all genotypes. The apo A-I content of HDL was inversely related to the expression of human apo A-II, probably reflecting displacement of apo A-I by an excess of apo A-II. Thus, the molar ratios of apo A-II/A-I in HDL were significantly higher in fed as compared with fasted animals of the same transgenic line, while endogenous LCAT activity concomitantly decreased. The number and size of HDL particles decreased in direct proportion to the level of human apo A-II expression. Apo A-II was abundantly present in all HDL particles, in contrast to apo A-I mainly present in large ones. Two novel findings were the presence of pre-beta migrating HDL transporting only human apo A-II in the higher-expressing mice and the increase of plasma HDL concentrations by fasting in control and transgenic mice. These findings highlight the reciprocal modifications of VLDL and HDL induced by the feeding-fasting transition and the key role of the molar ratio of apo A-II/A-I as a determinant of HDL particle metabolism and pre-beta HDL formation.


Assuntos
Apolipoproteína A-II/sangue , Apolipoproteína A-I/sangue , Lipoproteínas HDL/sangue , Animais , Apolipoproteína A-II/genética , Arteriosclerose/sangue , Arteriosclerose/etiologia , Ingestão de Alimentos , Jejum , Expressão Gênica , Lipoproteínas de Alta Densidade Pré-beta , Humanos , Hiperlipoproteinemia Tipo IV/sangue , Hiperlipoproteinemia Tipo IV/genética , Lipoproteínas LDL/sangue , Lipoproteínas VLDL/sangue , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos CBA , Camundongos Transgênicos , Tamanho da Partícula
3.
Int J Tissue React ; 22(2-3): 67-78, 2000.
Artigo em Inglês | MEDLINE | ID: mdl-10937356

RESUMO

Our understanding of the in vivo metabolic functions of apoA-I and A-II has greatly advanced with the use of transgenic mice, but the physiological role of apoA-IV remains elusive. Both apoA-I and A-II are necessary for the structural stability of high-density lipoprotein (HDL). Structural differences exist between human and mouse A apoproteins because: i) human cholesterol ester transfer protein, lecithin cholesterol acyl transferase and phospholipid transfer protein interact better with human apoA-I; ii) human apoA-I and A-II, alone or in combination, form polydisperse instead of monodisperse HDL particles. Human apoA-II overexpression has highlighted its inhibitory effect on lipoprotein lipase and hepatic lipase, resulting in hypertriglyceridemia and concomitantly decreased HDL and apoA-I. After long-term challenge with an atherogenic diet, mice are less protected against lesion formation by human apoA-II, mouse apoA-II being overtly proatherogenic. On the other hand, human apoA-I confers great protection against lesion formation and causes reduction of preexisting lesions. Human apoA-IV is also protective, although the mechanisms by which this protection is achieved remain to be determined.


Assuntos
Apolipoproteína A-II/biossíntese , Apolipoproteína A-I/biossíntese , Apolipoproteínas A/biossíntese , Colesterol/metabolismo , Animais , Apolipoproteína A-I/genética , Apolipoproteína A-II/genética , Apolipoproteína A-II/fisiologia , Apolipoproteínas A/genética , Arteriosclerose , Transporte Biológico Ativo , Suscetibilidade a Doenças , Perfilação da Expressão Gênica , Homeostase , Humanos , Lipoproteínas HDL/sangue , Camundongos , Camundongos Knockout , Camundongos Transgênicos
4.
Curr Opin Lipidol ; 11(2): 149-53, 2000 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-10787176

RESUMO

Our understanding of HDL metabolism in vivo has greatly advanced from studies with transgenic animals. Interactions between HDL apolipoproteins, transfer proteins, lipolytic enzymes and receptors modulate HDL size, particle number and fractional catabolic rate. The protective effect of HDL on atherosclerosis depends on the combined actions of HDL proteins and the metabolism of apo B-lipoproteins.


Assuntos
Lipoproteínas HDL/genética , Camundongos Transgênicos/metabolismo , Animais , Apolipoproteína A-I/metabolismo , Apolipoproteína A-II/metabolismo , Humanos , Cinética , Lipase/metabolismo , Lipase Lipoproteica/metabolismo , Lipoproteínas HDL/fisiologia , Fígado/enzimologia , Camundongos , Camundongos Transgênicos/genética
5.
J Biol Chem ; 274(17): 11564-72, 1999 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-10206963

RESUMO

Two lines of transgenic mice, hAIItg-delta and hAIItg-lambda, expressing human apolipoprotein (apo)A-II at 2 and 4 times the normal concentration, respectively, displayed on standard chow postprandial chylomicronemia, large quantities of very low density lipoprotein (VLDL) and low density lipoprotein (LDL) but greatly reduced high density lipoprotein (HDL). Hypertriglyceridemia may result from increased VLDL production, decreased VLDL catabolism, or both. Post-Triton VLDL production was comparable in transgenic and control mice. Postheparin lipoprotein lipase (LPL) and hepatic lipase activities decreased at most by 30% in transgenic mice, whereas adipose tissue and muscle LPL activities were unaffected, indicating normal LPL synthesis. However, VLDL-triglyceride hydrolysis by exogenous LPL was considerably slower in transgenic compared with control mice, with the apparent Vmax of the reaction decreasing proportionately to human apoA-II expression. Human apoA-II was present in appreciable amounts in the VLDL of transgenic mice, which also carried apoC-II. The addition of purified apoA-II in postheparin plasma from control mice induced a dose-dependent decrease in LPL and hepatic lipase activities. In conclusion, overexpression of human apoA-II in transgenic mice induced the proatherogenic lipoprotein profile of low plasma HDL and postprandial hypertriglyceridemia because of decreased VLDL catabolism by LPL.


Assuntos
Apolipoproteína A-II/genética , Hipertrigliceridemia/genética , Lipoproteínas VLDL/sangue , Animais , Apolipoproteína A-II/sangue , Feminino , Humanos , Hipertrigliceridemia/sangue , Lipase Lipoproteica/sangue , Lipoproteínas HDL/sangue , Fígado/enzimologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos CBA , Camundongos Transgênicos , Isoformas de Proteínas/sangue , Isoformas de Proteínas/genética
6.
J Biol Chem ; 274(8): 4954-61, 1999 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-9988739

RESUMO

Spatial gene expression in the intestine is mediated by specific regulatory sequences. The three genes of the apoA-I/C-III/A-IV cluster are expressed in the intestine following cephalocaudal and crypt-to-villus axes. Previous studies have shown that the -780/-520 enhancer region of the apoC-III gene directs the expression of the apoA-I gene in both small intestinal villi and crypts, implying that other unidentified elements are necessary for a normal intestinal pattern of apoA-I gene expression. In this study, we have characterized transgenic mice expressing the chloramphenicol acetyltransferase gene under the control of different regions of the apoC-III and apoA-IV promoters. We found that the -890/+24 apoC-III promoter directed the expression of the reporter gene in crypts and villi and did not follow a cephalocaudal gradient of expression. In contrast, the -700/+10 apoA-IV promoter linked to the -500/-890 apoC-III enhancer directed the expression of the reporter gene in enterocytes with a pattern of expression similar to that of the endogenous apoA-IV gene. Furthermore, linkage of the -700/-310 apoA-IV distal promoter region to the -890/+24 apoC-III promoter was sufficient to restore the appropriate pattern of intestinal expression of the reporter gene. These findings demonstrate that the -700/-310 distal region of the apoA-IV promoter contains regulatory elements that, in combination with proximal promoter elements and the -500/-890 enhancer, are necessary and sufficient to restrict apoC-III and apoA-IV gene expression to villus enterocytes of the small intestine along the cephalocaudal axis.


Assuntos
Apolipoproteínas A/genética , Apolipoproteínas C/genética , Elementos Facilitadores Genéticos , Regulação da Expressão Gênica , Animais , Apolipoproteína C-III , Cloranfenicol O-Acetiltransferase/genética , Intestino Delgado/metabolismo , Camundongos , Camundongos Transgênicos , RNA Mensageiro/genética , Sequências Reguladoras de Ácido Nucleico
7.
Eur J Biochem ; 253(1): 328-38, 1998 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-9578492

RESUMO

To assess the functional properties of apolipoprotein (apo) AII and to investigate the mechanism leading to the displacement of apo AI from native and reconstituted high-density lipoproteins (HDL and r-HDL) by apo AII, wild-type and variant apo AII peptides were synthesized. The wild-type peptides, residues 53-70 and 58-70, correspond to the C-terminal helix of apo AII and are predicted to insert at a tilted angle into a lipid bilayer. We demonstrate that both the apo AII-(53-70) peptide, and to a lesser extent the apo AII-(58-70) peptide are able to induce fusion of unilamellar lipid vesicles together with membrane leakage, and to displace apo AI from HDL and r-HDL. Two variants of the apo AII-(53-70)-wild-type (WT) peptide, designed either to be parallel to the water/lipid interface [apo AII-(53-70)-0 degrees] or to retain an oblique orientation [apo AII-(53-70)-30 degrees], were synthesized in order to test the influence of the obliquity on their fusogenic properties and ability to displace apo AI from HDL. The parallel variant did not bind lipids, due to its self-association properties. However, the apo AII-(53-70)-30 degrees variant was fusogenic and promoted the displacement of apo AI from HDL. Moreover, the extent of fusion of the apo AII-(53-70)-WT, apo AII-(58-70)-WT and apo AII-(53-70)-30 degrees peptides was related to the alpha-helical content of the lipid-bound peptides measured by infrared spectroscopy. Infrared measurements using polarized light also confirmed the oblique orientation of the helical component of the three peptides. In native and r-HDL, the tilted insertion of the C-terminal helix of apo AII resulting in a partial destabilization of the HDL external lipid layer might contribute to the displacement of apo AI by apo AII.


Assuntos
Apolipoproteína A-II/metabolismo , Apolipoproteína A-II/farmacologia , Apolipoproteína A-I/metabolismo , Lipoproteínas HDL/metabolismo , Fusão de Membrana/efeitos dos fármacos , Sequência de Aminoácidos , Apolipoproteína A-II/química , Humanos , Técnicas In Vitro , Lipossomos , Modelos Moleculares , Dados de Sequência Molecular , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Fragmentos de Peptídeos/farmacologia , Conformação Proteica , Estrutura Secundária de Proteína
8.
Am J Physiol ; 271(6 Pt 1): E952-64, 1996 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-8997212

RESUMO

Hepatocytes from obese and lean Zucker rats adapted to a control (C) or a high-fat (HF) diet were prepared for the study of fatty acid (FA) uptake, partition between oxidation and esterification, and very low density lipoprotein (VLDL) production. A first 2-h kinetic study showed higher oleate uptake on a C diet by obese rat cells and an almost exclusive esterification to triacylglycerol (TG), VLDL secretion being 2.5-fold higher in obese rat cells and enhanced 1.4-fold in both genotypes in the presence of 0.7 mM oleate vs. 0.1 mM or no oleate. Fat feeding 1) decreased oleate uptake, esterification, incorporation into VLDL-TG, and mass VLDL-TG secretion and 2) abolished the VLDL-TG increase by 0.7 mM oleate. Similar but more pronounced effects were obtained in fat-fed lean animals. A second kinetic study using very short incubation times up to 1 h confirmed that fat feeding decreased oleate uptake and esterification, greatly stimulating its oxidation and production of acetoacetate (obese) or acetoacetate and beta-hydroxybutyrate (lean). Synthesis of lactate and pyruvate greatly decreased under HF feeding, remaining higher in obese rat cells. The drastic inhibition of labeled and total hepatic VLDL-TG secretion in obese and lean Zucker rats by the HF diet could be partly explained by decreased exogenous FA availability for VLDL-TG synthesis through its greater channeling toward oxidation and, indirectly, by the altered hepatocyte metabolic state.


Assuntos
Gorduras na Dieta/administração & dosagem , Ácidos Graxos/administração & dosagem , Lipoproteínas VLDL/metabolismo , Fígado/metabolismo , Obesidade/metabolismo , Ratos Zucker , Animais , Ratos
9.
Eur J Biochem ; 242(3): 657-64, 1996 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-9022694

RESUMO

Human apolipoprotein A-II (apo A-II) consists of three potential amphipathic helices of 17 residues each, which contribute to the lipid-binding properties of this apolipoprotein. The conformation and lipid-binding properties of these peptides, either as single-helix or as two-helix peptides, were investigated by turbidity, fluorescence, electron-microscopy and circular-dichroism measurements, and are compared in this article. The lipid affinity of shorter C-terminal segments of apo A-II was compared with those of the single-helix or two-helix peptides, to define the minimal peptide length required for stable complex formation. The properties of the apo-A-II-(13-48)-peptide were further compared with those of the same segment after deletion of the Ser31 and Pro32 residues, because the deleted apo-A-II-(13-30)-(33-48)-peptide, is predicted to form a long uninterrupted helix. The single helices of apo A-II could not form stable complexes with phospholipids, and the helix-turn-helix segment spanning residues 13-48 was not active either. The apo-A-II-(37-77)-peptide and the apo-A-II-(40-73)-peptide could form complexes with lipids, which appear as discoidal particles by negative-staining electron microscopy. The shortest C-terminal domain of apo A-II able to associate with lipids to form stable complexes was the apo-A-II-(40-73)-peptide, which consisted of the C-terminal helix, a beta-turn and part of the preceding helix. The shorter apo-A-II-(49-77)-peptide, and the helical apo-A-II-(13-30)-(33-48)-peptide, could also associate with phospholipids. The complexes formed were, however, less stable, as they dissociated outside the transition temperature range of the phospholipid. These data suggest that the C-terminal pair of helices of apo A-II, which is the most hydrophobic pair, is responsible for the lipid-binding properties of the entire protein. The N-terminal pair of helices of apo A-II at residues 13-48 does not associate tightly with lipids. The degree of internal similarity and the cooperativity between the helical segments of apo A-II is thus less pronounced than in apo A-I or apo A-IV. The N-terminal and C-terminal domains of apo A-II appear to behave as two distinct entities with regard to lipid-protein association.


Assuntos
Apolipoproteína A-II/metabolismo , Sequência de Aminoácidos , Apolipoproteína A-II/química , Humanos , Microscopia Eletrônica , Modelos Moleculares , Dados de Sequência Molecular , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Fosfolipídeos/química , Ligação Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Relação Estrutura-Atividade
10.
Metabolism ; 44(1): 19-29, 1995 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-7854160

RESUMO

The effect of a high-protein (HP) diet on hepatic very-low-density lipoprotein (VLDL) secretion was studied in obese and lean Zucker rats. With the control (C) diet, isolated hepatocytes from obese as compared with lean rats displayed higher uptake of [1-14C]oleate 0.7 mmol/L, 95% of which was esterified to glycerolipids; greater oleate incorporation into VLDL-triacylglycerol (TG); 2.6 times higher total VLDL-TG secretion; and 11-fold higher de novo fatty acid synthesis. Adaptation to HP feeding decreased weight gains in both phenotypes and hepatocyte TG content in obese rats. Oleate uptake by hepatocytes was appreciably reduced in the obese phenotype only. Despite esterification rates similar to those for the C diet, oleate incorporation into VLDL-TG decreased by 34% and 55% in obese and lean rats, respectively. Total (mass) VLDL-TG secretion was drastically decreased by 65% and 48% in obese and lean rat hepatocytes, respectively. HP feeding combined with overnight fasting accentuated the above decreases. Fatty acid synthesis was 50% lower in cells from HP-fed obese rats, but increased 1.7-fold in lean ones. Plasma glucagon increased in both phenotypes under HP feeding, whereas plasma insulin either increased (obese) or decreased (lean), with the insulin to glucagon ratio slightly decreasing. Thus, HP feeding drastically inhibited hepatic VLDL secretion in obese and lean Zucker rats by an undefined mechanism that was apparently related neither to de novo fatty acid synthesis nor to changes in oleate partitioning between esterification and oxidation.


Assuntos
Adaptação Fisiológica , Proteínas Alimentares/farmacologia , Lipoproteínas LDL/metabolismo , Fígado/metabolismo , Obesidade/metabolismo , Animais , Peso Corporal , Ácidos Graxos/metabolismo , Glucagon/sangue , Insulina/sangue , Metabolismo dos Lipídeos , Lipoproteínas VLDL/metabolismo , Masculino , Obesidade/patologia , Ácido Oleico , Ácidos Oleicos/metabolismo , Ácidos Oleicos/farmacocinética , Ratos , Ratos Zucker , Triglicerídeos/metabolismo
11.
Biochemistry ; 33(13): 4056-64, 1994 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-8142408

RESUMO

It has been shown previously that apoA-II undergoes several intracellular modifications in HepG2 cells (Hussain & Zannis, 1990). In the present study, we have generated permanent cell lines in mouse C127 cells which express the normal apoA-II gene and a mutated form in which Gln+1 was substituted with Leu (Leu+1). This modification was designed to prevent cyclization of the N-terminal glutamine of apoA-II and thus identify the isoproteins which are precursors and products of the N-terminal cyclization reaction. The C127-expression cells were also utilized to study the cellular compartments where the apoA-II modifications occur as well as the importance of the modifications for apoA-II trafficking and secretion. We have found that apoA-II (Gln+1) synthesized by C127 and HepG2 cells had similar isoproteins. In both cell types, unmodified pro-apoA-II, designated isoprotein 3, had a similar isoelectric point as the cell-free translation product of apoA-II mRNA, suggesting that isoprotein 3 results from cleavage of the signal peptide. Isoprotein 3 represents an unmodified apoA-II isoprotein and undergoes an early modification into a more acidic isoprotein 1, which differs from isoprotein 3 by two negative charges. Brefeldin A treatment of the cells did not prevent the formation of isoprotein 1, suggesting that this modification occurs in a pre-Golgi compartment. Neuraminidase treatment of secreted apoA-II isoproteins did not affect isoprotein 1, indicating that it is not sialylated isoprotein. Isoprotein 1 undergoes further modifications which are consistent with cleavage of the propeptide, N-terminal cyclization and sialylation most likely resulting from O-glycosylation.(ABSTRACT TRUNCATED AT 250 WORDS)


Assuntos
Apolipoproteína A-II/metabolismo , Eletroforese em Gel Bidimensional , Retículo Endoplasmático/metabolismo , Glicosilação , Complexo de Golgi/metabolismo , Humanos , Mutagênese Sítio-Dirigida , Neuraminidase/farmacologia , Processamento de Proteína Pós-Traducional , Proteínas Recombinantes , Relação Estrutura-Atividade
12.
Am J Physiol ; 263(4 Pt 1): E615-23, 1992 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-1415680

RESUMO

Triacylglycerol (TG) stored in cytoplasmic lipid droplets of hepatocytes was labeled by in vivo [1-(14)C]oleic acid injection to study the effect of a high-fat diet on its incorporation into very-low-density lipoproteins (VLDL). Compared with the control diet, hepatocytes of fat-fed rats 1) contained 7.6 times more cytoplasmic (floating fat) TG and 1.9 times more endoplasmic reticulum (microsomal) TG; 2) had 8 and 6 times lower TG specific activities in cytoplasm and endoplasmic reticulum, respectively; 3) incorporated 22% less 14C label into hepatocyte esterified lipids (TG, cholesterol, phospholipid); 4) secreted 48 and 33% less radioactive and total VLDL-TG, respectively; 5) oxidized more cytoplasmic TG-fatty acid (FA); and 6) showed a 50% decreased total utilization of stored TG-FA. With both diets, the lysosomal inhibitor chloroquine concomitantly decreased productions of labeled VLDL-TG, CO2, and acid-soluble oxidation products. The decreased incorporation of stored TG into VLDL-TG appreciably contributes to the overall inhibition of hepatic VLDL secretion by fat feeding. It appears to be related to the decreased mobilization rate of stored TG and its increased channelling toward oxidation.


Assuntos
Gorduras na Dieta/farmacologia , Lipoproteínas VLDL/metabolismo , Fígado/metabolismo , Triglicerídeos/metabolismo , Animais , Radioisótopos de Carbono , Meios de Cultura , Citoplasma/metabolismo , Retículo Endoplasmático/metabolismo , Metabolismo dos Lipídeos , Lipídeos/química , Fígado/citologia , Masculino , Oxirredução , Proteínas/química , Proteínas/metabolismo , Ratos , Ratos Wistar
14.
Biochim Biophys Acta ; 1002(1): 28-36, 1989 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-2923863

RESUMO

The cytoplasmic triacylglycerol (TG) storage pool of isolated hepatocytes was labelled in order to evaluate its incorporation into very low density lipoproteins (VLDL). Rats were injected with [1-14C]oleate 2 min prior to surgery and cell incubations began 90-100 min thereafter. In keeping with the equilibration of the two TG pools (in smooth endoplasmic reticulum, SER, and cytoplasm) in 120 min (Stein, Y. and Shapiro, B. (1959) Am. J. Physiol. 196, 1238-1241) the bulk of radioactive TG at time zero was in the cytoplasm and TG specific activities were similar in cytoplasm and SER. Radioactive and total VLDL-TG secretions were greatly inhibited after 80 min by chloroquine which is assumed to block lysosomal hydrolysis of cytoplasmic TG. When the SER-TG pool was labelled by addition of [1-14C]oleate in vitro, chloroquine affected neither [1-14C]oleate uptake and esterification nor its incorporation into VLDL-TG from 15-20 min until 80 min. After 100 min, when [1-14C]oleate-TG was transferred back from cytoplasm to SER, chloroquine began to decrease radioactive VLDL-TG output and by 210 min caused the same inhibition as under the in vivo labelling condition. These results are consistent with an inhibition by chloroquine of the lysosomal hydrolysis of cytoplasmic TG resulting in a blockage of their back transfer to SER membranes whereas other steps of VLDL production were not affected, at least up to 100 min. This study also showed that stored TG is a quantitatively important VLDL precursor, sustaining VLDL production for several hours in the absence of exogenous fatty acids.


Assuntos
Citoplasma/metabolismo , Lipoproteínas VLDL/metabolismo , Fígado/metabolismo , Triglicerídeos/metabolismo , Animais , Radioisótopos de Carbono , Cloroquina/farmacologia , Retículo Endoplasmático/metabolismo , Esterificação , Complexo de Golgi/metabolismo , Cinética , Fígado/efeitos dos fármacos , Masculino , Microssomos Hepáticos/metabolismo , Ácido Oleico , Ácidos Oleicos/metabolismo , Ratos , Ratos Endogâmicos
15.
Biochim Biophys Acta ; 959(1): 76-83, 1988 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-3345312

RESUMO

The objectives of this study were to measure intestinal very-low-density lipoprotein (VLDL) production in obese Zucker rats and to assess an eventual effect of a high-fat diet. VLDL secretion was specifically inhibited by orotic acid, and intestinal VLDL output was measured following the Triton WR-1339 method. After a control diet, total VLDL secretion (without orotic acid) was 4.8 +/- 0.3 and 1.4 +/- 0.1 mg triacylglycerol/ml in obese and lean rats, respectively, decreasing by 30% in obese rats after fat-feeding. Intestinal VLDL production was similar in obese and lean rats fed the control diet (0.32 +/- 0.05 and 0.27 +/- 0.05 mg triacylglycerol/ml, respectively), increasing 2.5-fold after fat-feeding in both genotypes. Thus, intestine contributed 21 and 60% of total VLDL in lean but only 7 and 24% in obese rats with the control and high-fat diets, respectively. These results show that the intestine of obese Zucker rats does not contribute to their hypertriglyceridemia, suggesting that it originates solely from liver. Moreover, their intestinal VLDL production was stimulated by fat-feeding to the same extent as in lean animals.


Assuntos
Mucosa Intestinal/metabolismo , Lipoproteínas VLDL/biossíntese , Fígado/metabolismo , Animais , Peso Corporal/efeitos dos fármacos , Quilomícrons/biossíntese , Quilomícrons/metabolismo , Dieta , Gorduras na Dieta , Feminino , Intestinos/efeitos dos fármacos , Lipoproteínas VLDL/metabolismo , Fígado/efeitos dos fármacos , Masculino , Ácido Orótico/farmacologia , Ratos , Ratos Zucker , Valores de Referência
16.
Reprod Nutr Dev (1980) ; 25(1B): 227-34, 1985.
Artigo em Francês | MEDLINE | ID: mdl-3991992

RESUMO

Hepatic VLDL production appears to be correlated with de novo fatty acid synthesis (lipogenesis). In this study lipogenesis was inhibited in vitro in order to establish an eventual direct effect on VLDL secretion. Hepatocytes from rats fed a standard diet were incubated with three triglyceride-rich lipoproteins: chylomicrons and VLDL obtained from rats fed a high-fat diet and VLDL obtained from rats fed a standard diet. The inhibition of lipogenesis (10 to 55%) was proportional to the concentration of the lipoproteins added. Chylomicrons and VLDL originating mainly from the intestine (prepared from fat-fed rats) inhibited lipogenesis more effectively than VLDL produced essentially by the liver (prepared from rats fed a standard diet). However the secretion of newly synthesized fatty acids in the medium did not decrease. When hepatocyte lipogenesis was inhibited by the addition of 1 mM oleic acid, total VLDL secretion (expressed as nmol of VLDL triglyceride/10(6) cells) was unchanged compared to control cells incubated without oleic acid. Our results suggest that hepatic VLDL secretion is not directly related to de novo fatty acid synthesis.


Assuntos
Ácidos Graxos/biossíntese , Lipoproteínas VLDL/farmacologia , Fígado/metabolismo , Animais , Quilomícrons/farmacologia , Gorduras na Dieta/farmacologia , Lipoproteínas VLDL/metabolismo , Fígado/efeitos dos fármacos , Masculino , Ácido Oleico , Ácidos Oleicos/farmacologia , Ratos , Ratos Endogâmicos
17.
Metabolism ; 32(7): 661-8, 1983 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-6865756

RESUMO

The uptake and metabolism of [1-14C]oleate (0.3 mmol/L) were studied in isolated hepatocytes from lean and obese Zucker rats fed either a control (low-fat) diet or a high-fat diet. With the control diet, [1-14C]oleate uptake was increased by 70% in the obese rats, and fat-feeding decreased this uptake to values comparable to that of their lean littermates. Interestingly, the hepatocyte mean surface area was increased in the obese mutants by 21% with the control diet and by 30% with the high-fat diet. The possible reasons for the differences in oleate uptake are discussed. With the control diet, cells from the obese rats showed a four-fold rise in [1-14C]oleate esterification, while ketogenesis (beta-hydroxybutyrate + acetoacetate production) as well as the radioactive acid-soluble products were greatly depressed. Production of CO2 was very low and similar in both groups of animals. Adaptation to the high-fat diet in the obese rats resulted in a reversal between esterification and oxidation of oleate: the latter became the major metabolic pathway as in the lean rats. The ketogenic capacity was greatly if not completely restored. In the lean animals, glucagon stimulated ketogenesis both in the presence or absence of oleate and decreased [1-14C]oleate esterification. In the obese rats, the hormone exerted a significant ketogenic effect only if oleate was present and did not influence its esterification. The data demonstrate the following abnormalities in the hepatocytes of obese Zucker rats: (1) an enlargement of cell size, (2) an increased oleate uptake, (3) a virtual absence of a ketogenic response to exogenous oleate, and (4) a markedly increased esterification of the latter. The metabolic defects, but not the cell size, appear to be largely corrected by an adaptation to a high-fat diet. The hepatic response to glucagon was decreased in the obese rats at the level of endogenous ketogenesis.


Assuntos
Gorduras na Dieta/farmacologia , Glucagon/farmacologia , Fígado/metabolismo , Obesidade/metabolismo , Ácidos Oleicos/metabolismo , Animais , Técnicas In Vitro , Cetonas/biossíntese , Fígado/citologia , Masculino , Ácido Oleico , Ratos , Ratos Zucker
18.
Biochim Biophys Acta ; 711(1): 33-9, 1982 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-7066371

RESUMO

1. The effect of a high-fat diet (30% fat by wt.) on intestinal very low density lipoprotein (VLDL) secretion was studied in male rats after specific inhibition of hepatic VLDL secretion by dietary orotic acid. Total VLDL secretion (from liver and intestine) was measured in animals not receiving orotic acid. 2. Fat-feeding resulted in a 32% decreased post-Triton secretion of total serum VLDL triacylglycerols as compared to a control (low fat) diet. Concomitantly, a large stimulation of post-Triton intestinal VLDL triacylglycerols secretion was measured in fat-fed rats. Thus, the major part (64%) of circulating triacylglycerols transported as VLDL originated from the intestine in these animals, leading presumably to an increased secretion of intestinal apolipoproteins. 3. Intestinal VLDL and chylomicron secretion rates increased with the amount of fat in the diet (7, 13, 20 or 30% fat by wt.). Whereas the chylomicron secretion was linearly related to the dietary fat content, the relationship between intestinal VLDL secretion and fat content of the diet was sigmoidal. The highest stimulation of intestinal VLDL formation was observed within a narrow range of dietary fat content (between 10 and 20%).


Assuntos
Gorduras na Dieta/administração & dosagem , Secreções Intestinais/efeitos dos fármacos , Lipoproteínas VLDL/metabolismo , Animais , Quilomícrons/metabolismo , Gorduras na Dieta/farmacologia , Fígado/metabolismo , Masculino , Ácido Orótico/farmacologia , Polietilenoglicóis/farmacologia , Ratos , Ratos Endogâmicos
19.
Biochem J ; 198(2): 373-7, 1981 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-7326012

RESUMO

The very-low-density-lipoprotein secretion rate of isolated hepatocytes obtained from rats fed a high-fat diet was half that of cells from control animals. In fat-fed rats, the initial cellular uptake of [l-14C]oleate in vitro was decreased by 25%, its esterification to triacylglycerols and phospholipids by 50% and its incorporation into very-low-density-lipoprotein triacylglycerols by 70%. Exogenous oleate was not the main precursor of very-low-density lipoproteins in these animals. Lipogenesis, a minor source of very-low-density lipoproteins with the control diet in our experimental conditions, was inhibited by 84% after fat-feeding. A short-term inhibition of lipogenesis in vitro did not result in a decrease in very-low-density-lipoprotein secretion rate. The results suggest that fat-feeding decreased availability of exogenous as well as endogenous fatty acids for synthesis of very-low-density lipoproteins.


Assuntos
Gorduras na Dieta/farmacologia , Lipoproteínas VLDL/metabolismo , Fígado/metabolismo , Animais , Esterificação , Técnicas In Vitro , Lipídeos/biossíntese , Fígado/citologia , Fígado/efeitos dos fármacos , Masculino , Ácido Oleico , Ácidos Oleicos/metabolismo , Ratos , Ratos Endogâmicos
20.
Biochim Biophys Acta ; 620(1): 111-9, 1980 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-7417475

RESUMO

1. Very low density lipoprotein (VLDL) secretion rates were studied on rats adapted to a high-fat diet (71% calories as lard) for 3-4 weeks, compared to control (starch-fed) rats. 2. Experiments were performed at 14.00 h, at which time all animals had the same circulating free fatty acids. Fat-fed rats presented an apparent liver stealosis, a high post-Triton chylomicron secretion, but a 40% decreased VLDL secretion. 3. Injection of [1-14C]palmitic acid showed that the tracer was incorporated less in liver triacylglycerols of the fat-fed rats, presumably because of an enhanced ketogenesis. Secretion of labelled VLDL-triacylglycerols in 1 h was diminished 5-fold, even after a correction for the lower hepatic esterification. 4. Two complementary experiments were carried out, with the following results: at 08.00 h, when serum free fatty acid concentrations were comparable in both groups of rats [5,10], post-Triton VLDL secretion was diminished by 45% in the fat-fed rats; at 20.00 h, the fat-fed rats had significantly elevated plasma free fatty acids [5,10], but their VLDL secretion was the same as in control rats. 5. So it appears that in fat-fed rats circulating free fatty acids do not stimulate VLDL secretion as expected. It is suggested that the decreased VLDL secretion with the high-fat diet may result from inhibition of hepatic lipogenesis.


Assuntos
Gorduras na Dieta/metabolismo , Lipoproteínas VLDL/metabolismo , Animais , Quilomícrons/metabolismo , Gorduras na Dieta/administração & dosagem , Jejum , Ácidos Graxos não Esterificados/metabolismo , Masculino , Ratos
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