Patsch W, Franz S, Schonfeld G
J Clin Invest. 1983 May;71(5):1161-74. doi: 10.1172/jci110865.
To study the effect of insulin on lipoprotein synthesis and secretion by the liver, apoprotein and lipid levels were measured in primary rat liver cell cultures grown on fibronectin-coated dishes. Triglycerides, phospholipids, apoprotein (apo) B, apo-E, and apo-C-III3 all accumulated in culture media linearly for periods up to 20 h. During incubations, cellular triglyceride contents increased slightly, while cellular apoprotein and phospholipid contents remained constant. In the absence of insulin, rates of accumulation in media of triglycerides, apo-B, apo-C-III3, and apo-E were 2.5 +/- 0.3 micrograms/mg and 33 +/- 5, 24 +/- 3, and 162 +/- 32 ng/mg cell protein per h, respectively. On gel permeation chromatography and density gradient ultracentrifugation, the majority of apoproteins in media were found to be associated with very low density lipoproteins (VLDL) and very little eluted or sedimented with albumin. Incubations in the presence of 50-800 microU/ml of insulin resulted in dose-dependent decreases of triglyceride, phospholipid, apo-B, and apo-E accumulation in the media, paralleled by increases in the cellular contents of these lipoprotein components. The inhibitory effects of insulin on secretion were reversible. Levels of apo-C-III3 and albumin were not affected by insulin. In addition to decreasing secretory rates, the proportion of apo-B, apo-E, and apo-C-III3 associated with VLDL also decreased after the addition of insulin. Concomitantly, the proportion of apo-B eluting with LDL and apo-C-III3, and apo-E eluting near albumin increased. Control experiments, in which exogenous 125I-VLDL or endogenously labeled [14C]VLDL were added to cultures, revealed that the insulin-induced differences in VLDL accumulation and the lipid association of media apoproteins were not due to differences in the processing of VLDL by cells cultured in the presence or absence of insulin. Therefore, it appears that insulin may inhibit the secretion of VLDL perhaps by reducing the intracellular association of lipids and apoproteins.
为研究胰岛素对肝脏脂蛋白合成与分泌的影响，在纤连蛋白包被培养皿上培养的原代大鼠肝细胞中测量了载脂蛋白和脂质水平。甘油三酯、磷脂、载脂蛋白（apo）B、apo-E和apo-C-III3在培养基中均线性累积长达20小时。在孵育过程中，细胞内甘油三酯含量略有增加，而细胞内载脂蛋白和磷脂含量保持不变。在无胰岛素的情况下，甘油三酯、apo-B、apo-C-III3和apo-E在培养基中的累积速率分别为每小时2.5±0.3微克/毫克细胞蛋白和33±5、24±3、162±32纳克/毫克细胞蛋白。在凝胶渗透色谱和密度梯度超速离心分析中，发现培养基中的大多数载脂蛋白与极低密度脂蛋白（VLDL）相关，很少与白蛋白一起洗脱或沉淀。在50 - 800微单位/毫升胰岛素存在下孵育导致培养基中甘油三酯、磷脂、apo-B和apo-E累积呈剂量依赖性降低，同时这些脂蛋白成分的细胞内含量增加。胰岛素对分泌的抑制作用是可逆的。apo-C-III3和白蛋白水平不受胰岛素影响。除了降低分泌速率外，添加胰岛素后与VLDL相关的apo-B、apo-E和apo-C-III3的比例也降低。同时，与低密度脂蛋白（LDL）一起洗脱的apo-B以及与白蛋白附近洗脱的apo-C-III3和apo-E的比例增加。对照实验中，将外源性125I-VLDL或内源性标记的[14C]VLDL添加到培养物中，结果表明胰岛素诱导的VLDL累积差异以及培养基载脂蛋白的脂质结合差异并非由于在有或无胰岛素条件下培养的细胞对VLDL的处理差异所致。因此，似乎胰岛素可能通过减少脂质和载脂蛋白的细胞内结合来抑制VLDL的分泌。
