Bell-Quint J, Forte T
Biochim Biophys Acta. 1981 Jan 26;663(1):83-98. doi: 10.1016/0005-2760(81)90196-x.
Lipoproteins in the three major density classes were isolated from the medium of cultured rat hepatocytes incubated in the absence of serum for periods ranging from 1 to 48 h. De novo synthesis was suggested by the cycloheximide-sensitive incorporation of [3H]leucine into the apolipoproteins of the secreted lipoproteins. Hepatocyte d less than 1.006 and d 1.006-1.063 g/ml lipoproteins were similar to plasma very low density lipoprotein (VLDL) and low density lipoprotein (LDL), respectively, in chemical composition, morphology and apolipoprotein distribution. The isolation of plasma-like d 1.006-1.063 g/ml particles is evidence for the hepatic origin of rat LDL; however, whether these particles are synthesized directly or result from catabolism of secreted VLDL has not been determined. Spherical d 1.063-1.21 g/ml particles containing predominantly apolipoprotein A-I were isolated from the media. In contrast to plasma high density lipoprotein (HDL) the hepatocyte particles contained significant concentrations of triacylglycerol and apolipoproteins of Mr greater than 100,000 and lacked apolipoprotein A-IV. The pattern of lipoprotein secretion was related to the time of incubation. After incubation for 1, 3 and 6.5 h, VLDL comprised approx. 56% of the total lipoprotein mass, LDL 20% and HDL 24%. After 17 and 48 h the VLDL concentration was greatly reduced (approx. 20% of the total mass) while LDL and HDL concentrations were increased (33 and 47% of the total, respectively). Exogenous sodium oleate resulted in a concentration-dependent stimulation of VLDL synthesis at longer incubation periods. The triacylglycerol content of the secreted LDL fraction was also significantly increased following sodium oleate addition and there was an increased number of 425-650 A particles present, which may represent catabolic products of VLDL. Hepatocyte monolayers which can be maintained in serum-free media for extended period should be useful for studying regulation of hepatic metabolism of the three major lipoprotein classes.
从无血清培养1至48小时的大鼠肝细胞培养基中分离出三类主要密度的脂蛋白。[3H]亮氨酸对分泌型脂蛋白载脂蛋白的环己酰亚胺敏感掺入表明了从头合成。密度小于1.006 g/ml和1.006 - 1.063 g/ml的肝细胞脂蛋白分别在化学组成、形态和载脂蛋白分布上与血浆极低密度脂蛋白（VLDL）和低密度脂蛋白（LDL）相似。分离出类血浆的密度为1.006 - 1.063 g/ml的颗粒证明大鼠LDL起源于肝脏；然而，这些颗粒是直接合成的还是由分泌的VLDL分解代谢产生的尚未确定。从培养基中分离出主要含载脂蛋白A-I的球形密度为1.063 - 1.21 g/ml的颗粒。与血浆高密度脂蛋白（HDL）相比，肝细胞颗粒含有大量三酰甘油和分子量大于100,000的载脂蛋白，且缺乏载脂蛋白A-IV。脂蛋白分泌模式与孵育时间有关。孵育1、3和6.5小时后，VLDL约占总脂蛋白质量的56%，LDL占20%，HDL占24%。孵育17和48小时后，VLDL浓度大幅降低（约占总质量的20%），而LDL和HDL浓度增加（分别占总质量的33%和47%）。在较长孵育期，外源性油酸钠导致VLDL合成呈浓度依赖性刺激。添加油酸钠后，分泌的LDL部分的三酰甘油含量也显著增加，并且存在数量增加的425 - 650 Å颗粒，这可能代表VLDL的分解代谢产物。能够在无血清培养基中长时间维持的肝细胞单层对于研究三种主要脂蛋白类别的肝脏代谢调节应该是有用的。
