Svedberg J, Björntorp P, Smith U, Lönnroth P
Department of Medicine, Sahlgren's Hospital, University of Göteborg, Sweden.
Diabetes. 1992 Mar;41(3):294-8. doi: 10.2337/diab.41.3.294.
We demonstrated previously that high physiological concentrations of free fatty acids (FFA) rapidly decrease insulin binding, degradation, and action in isolated rat hepatocytes. In this study, hepatocytes from lean and obese Sprague-Dawley rats (Alab, Stockholm) were preincubated with or without 0.4 mM oleic acid, and the effect on insulin binding and tyrosine kinase activity was measured. In the absence of exogenous FFA, insulin binding was reduced in hepatocytes from obese compared with lean rats (mean +/- SE reduction 44 +/- 7%, n = 8, P less than 0.01). Furthermore, the inhibitory effect of oleic acid added to hepatocytes from lean rats (n = 8; 40 +/- 9%, P less than 0.01) was not seen in cells from obese rats. Treating obese rats with Etomoxir, a carnitine palmitoyl transferase I inhibitor, increased insulin binding to isolated hepatocytes by 41 +/- 13% (n = 5, P less than 0.05). There was no difference in total binding to partially purified insulin receptors from solubilized hepatocytes from lean and obese rats, whether cells were or were not preincubated with oleic acid. Tyrosine kinase activity of partially purified receptors from basal or insulin-stimulated cells was not affected by either obesity, treatment with Etomoxir, or preincubating the cells with oleic acid. Thus, both obesity and elevated ambient FFA levels are associated with impaired insulin cell surface binding to isolated hepatocytes, possibly through an effect of lipid oxidation on the internalization/recycling of the insulin-receptor complex without any perturbation of the receptor tyrosine kinase activity. The data suggest that the reduced insulin binding to hepatocytes from obese rats is due to elevated ambient FFA levels.
我们先前已证明，高生理浓度的游离脂肪酸（FFA）可迅速降低分离的大鼠肝细胞中的胰岛素结合、降解及作用。在本研究中，将来自瘦型和肥胖型斯普拉格-道利大鼠（阿拉布，斯德哥尔摩）的肝细胞在有或无0.4 mM油酸的情况下进行预孵育，并测定其对胰岛素结合和酪氨酸激酶活性的影响。在无外源性FFA时，与瘦型大鼠相比，肥胖型大鼠肝细胞中的胰岛素结合减少（平均±标准误降低44±7%，n = 8，P < 0.01）。此外，添加到瘦型大鼠肝细胞（n = 8；40±9%，P < 0.01）中的油酸的抑制作用在肥胖型大鼠的细胞中未观察到。用肉碱棕榈酰转移酶I抑制剂依托莫昔治疗肥胖型大鼠，可使分离的肝细胞的胰岛素结合增加41±13%（n = 5，P < 0.05）。无论细胞是否用油酸预孵育，来自瘦型和肥胖型大鼠的溶解肝细胞与部分纯化的胰岛素受体的总结合均无差异。基础或胰岛素刺激细胞的部分纯化受体的酪氨酸激酶活性不受肥胖、依托莫昔治疗或细胞用油酸预孵育的影响。因此，肥胖和升高的环境FFA水平均与胰岛素在细胞表面与分离的肝细胞的结合受损有关，可能是通过脂质氧化对胰岛素-受体复合物的内化/再循环的影响，而不会对受体酪氨酸激酶活性产生任何干扰。数据表明，肥胖型大鼠肝细胞胰岛素结合减少是由于环境FFA水平升高所致。
