Hennes M M, Shrago E, Kissebah A H
Department of Medicine, Medical College of Wisconsin, Milwaukee 53226.
Int J Obes. 1990 Oct;14(10):831-41.
The effects of free fatty acids (FFA) on insulin receptor binding and processing (internalization, degradation, dissociation, and release) were examined in hepatocytes isolated from 12-week-old female rats. Animals were fasted for 24 h to deplete liver glycogen and lipid content. Cells were preincubated for 30 min or 3 h at 37 degrees C in media containing 10 mM lactate, 1 mM pyruvate, and 3.5 percent albumin with increasing concentrations of palmitate (0.00, 0.05, 0.2, 0.5, 1.0 and 2.0 mM). Under these conditions palmitate is the primary substrate for cellular metabolism, and its major fate is oxidation. Equilibrium binding was determined after 18-20 h of incubation at 4 degrees C with radiolabeled insulin and increasing concentrations of unlabeled hormone. With increasing palmitate concentration, a dose-dependent decline in cell-surface insulin receptor binding was observed. Binding decreased by 35 percent and 44 percent after 30 min and 3 h of preincubation with 2 mM palmitate, respectively. This decrease was due to a reduction in insulin receptor number. Receptor-mediated insulin processing was evaluated in cells prelabeled at 4 degrees C with 125I (A14)-monoiodoinsulin at an insulin concentration of 100 pM and reincubated at 37 degrees C for up to 30 min. The amount of internalized insulin was decreased by preincubation of hepatocytes with palmitate. This decrease was proportional to the reduction in cell-surface insulin receptor density at palmitate concentrations of 0.05-0.5 mM, but was disproportionally greater at higher fatty acid concentrations. Receptor-mediated insulin degradation decreased at palmitate concentrations between 0.05 and 1.0 mM. At 2 mM, however, insulin degradation was enhanced. This enhancement was observed after 30 min or 3 h of exposure to the fatty acid. Dissociation and/or release of cell-associated internalized insulin was not influenced by the FFA exposure. The effects of FFA on hepatocyte insulin binding and processing were contingent upon cellular metabolism, since no changes were noted when cells were preincubated with palmitate at 4 degrees C under otherwise similar conditions. Thus the in vitro exposure of hepatocytes to FFA influences both receptor and postreceptor events mediating insulin metabolism. These effects may account for the altered hepatic insulin extraction and sensitivity that accompany abdominal obesity and its progression to diabetes.
在从12周龄雌性大鼠分离的肝细胞中，研究了游离脂肪酸（FFA）对胰岛素受体结合及处理（内化、降解、解离和释放）的影响。动物禁食24小时以耗尽肝糖原和脂质含量。细胞在含有10 mM乳酸、1 mM丙酮酸和3.5%白蛋白且棕榈酸浓度递增（0.00、0.05、0.2、0.5、1.0和2.0 mM）的培养基中于37℃预孵育30分钟或3小时。在这些条件下，棕榈酸是细胞代谢的主要底物，其主要去向是氧化。在4℃用放射性标记胰岛素和递增浓度的未标记激素孵育18 - 20小时后测定平衡结合。随着棕榈酸浓度增加，观察到细胞表面胰岛素受体结合呈剂量依赖性下降。用2 mM棕榈酸预孵育30分钟和3小时后，结合分别下降了35%和44%。这种下降是由于胰岛素受体数量减少。在4℃用125I（A14）-单碘胰岛素以100 pM的胰岛素浓度对细胞进行预标记，并在37℃再孵育长达30分钟，以此评估受体介导的胰岛素处理。棕榈酸预孵育肝细胞会使内化胰岛素量减少。在棕榈酸浓度为0.05 - 0.5 mM时，这种减少与细胞表面胰岛素受体密度的降低成比例，但在较高脂肪酸浓度下不成比例地更大。在棕榈酸浓度为0.05至1.0 mM之间，受体介导的胰岛素降解减少。然而，在2 mM时，胰岛素降解增强。在暴露于脂肪酸30分钟或3小时后观察到这种增强。细胞相关内化胰岛素的解离和/或释放不受FFA暴露的影响。FFA对肝细胞胰岛素结合和处理的影响取决于细胞代谢，因为在其他条件相似的情况下，当细胞在4℃用棕榈酸预孵育时未观察到变化。因此，肝细胞在体外暴露于FFA会影响介导胰岛素代谢的受体及受体后事件。这些影响可能解释了腹部肥胖及其向糖尿病进展时肝脏胰岛素摄取和敏感性的改变。
