RESUMO
Metabolic profiling studies have highlighted increases in the plasma free fatty acid (FFA) and branched-chain amino acid (BCAA) concentrations, which are hallmarks of the obese and insulin-resistant phenotype. However, little is known about how the increase of the BCAA concentration modifies the metabolic fate of FFA, and vice versa, in adipocytes. Therefore, we incubated differentiated 3T3-L1 adipocytes or primary adipocytes from rats fed a control or a high-fat diet with: (1) 0, 250, 500 and 1000 µM of leucine and determined the oxidation and incorporation of [1-14C]-palmitate into lipids or proteins or (2) 0, 250, 500 or 1000 µM of palmitate and evaluated the oxidation and incorporation of [U-14C]-leucine into lipids or proteins. Leucine decreased palmitate oxidation and increased its incorporation into the lipid fraction in adipocytes; the latter was reduced in adipocytes from obese rats. However, palmitate increased leucine oxidation in adipocytes as well as reduced leucine incorporation into the protein and lipid fractions in adipocytes from obese rats. These results demonstrate that leucine modifies the metabolic fate of palmitate, and vice versa, in adipocytes and that the metabolic interaction between leucine and palmitate catabolism is altered in adipocytes from obese rats.
Assuntos
Adipócitos/metabolismo , Leucina/metabolismo , Obesidade/metabolismo , Palmitatos/metabolismo , Células 3T3-L1 , Adipócitos/efeitos dos fármacos , Animais , Carnitina O-Palmitoiltransferase/genética , Dieta Hiperlipídica/efeitos adversos , Relação Dose-Resposta a Droga , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Leucina/administração & dosagem , Leucina/farmacocinética , Metabolismo dos Lipídeos/efeitos dos fármacos , Masculino , Proteínas de Membrana Transportadoras/genética , Camundongos , Transportadores de Ácidos Monocarboxílicos , Obesidade/patologia , Palmitatos/administração & dosagem , Palmitatos/farmacocinética , Enzima Bifuncional do Peroxissomo/genética , Ratos Endogâmicos , Ratos Sprague-DawleyRESUMO
The scope of the present work was to investigate the metabolism and the passage of octanoate from albumin into the phospholipid bilayer of the plasma membrane and from thence into the cell space. The experiments were done in the isolated perfused rat liver with infusions of albumin and octanoate at various concentrations. Once steady-state conditions were attained, trace amounts of [1-14C]-octanoate, [131 I]-albumin and [3H]-water were injected simultaneously and the effluent perfusate was fractionated. The normalized dilution curves were used for model analysis. The model which gives the best fit to the experimental results and which also produces the most consistent parameters is one that presupposes a rapid distribution of octanoate into the cell membrane and a slow transfer from the cell membrane into the cytosol. The concentration dependence of the distribution between the membrane and the extracellular space is parabolic, suggesting that octanoate changes the properties of the cell membrane when present at higher concentrations. The passage from the cell membrane into the cell space is relatively slow and limits metabolic transformation partly or totally, depending on the octanoate concentration in the plasma membrane. The rapid transfer of octanoate from the albumin space into the plasma membrane corroborates previous measurements of the dissociation of the albumin-octanoate complex.
Assuntos
Caprilatos/farmacocinética , Espaço Extracelular , Fígado/metabolismo , Perfusão , Albuminas/farmacocinética , Animais , Transporte Biológico , Radioisótopos de Carbono , Membrana Celular/metabolismo , Cinética , Masculino , Modelos Biológicos , Palmitatos/farmacocinética , Ratos , Ratos WistarRESUMO
Unidirectional fluxes (influx and efflux) and the net flux of palmitate across the hepatocyte membrane were measured in the intact rat liver employing the multiple indicator dilution technique. At albumin concentrations in the range between 0.1 and 0.5 mM the influx rate was 2.3 times greater than that of the net flux. The rate of efflux was somewhat higher than the net flux, indicating that palmitate undergoes an exchange process across the liver cell membranes with efflux to the extracellular albumin site being significant. At lower albumin concentrations, however, the influx/net flux ratio approached unity, implying that transport becomes a rate-limiting factor for metabolism.