Rinninger F, Kaiser T, Windler E, Greten H, Fruchart J C, Castro G
Universität Hamburg, Krankenhaus Eppendorf, Medizinische Kernklinik und Poliklinik, Hamburg, Germany.
Biochim Biophys Acta. 1998 Aug 28;1393(2-3):277-91. doi: 10.1016/s0005-2760(98)00082-4.
Selective uptake of high-density lipoprotein (HDL)-associated cholesteryl esters (CE), i.e. lipid uptake independent of HDL particle uptake, delivers CE to the liver and steroidogenic tissues in vivo and in vitro. From human plasma HDL, two major subpopulations of particles can be isolated: one contains both apolipoprotein (apo) A-I and apo A-II (designated LpA-I:A-II) as dominant protein components, whereas in the other apo A-II is absent (LpA-I). In this study, selective CE uptake from LpA-I and LpA-I:A-II by cultured cells was investigated. LpA-I and LpA-I:A-II were isolated by immunoaffinity chromatography from human plasma high-density lipoprotein3 (HDL3, d = 1.125-1.21 g/ml) and both particles were radiolabeled in the protein (125I) as well as in the CE moiety ([3H]cholesteryl oleyl ether ([3H]CEt)). Several control experiments validated the labeling methodology applied. To investigate selective CE uptake, human Hep G2 hepatoma cells, human hepatocytes in primary culture and human skin fibroblasts were incubated in medium containing doubly radiolabeled LpA-I or LpA-I:A-II particles. Thereafter cellular tracer content was determined. For each cell type the rate of apparent lipoprotein particle uptake according to the lipid tracer ([3H]CEt) was in substantial excess over that due to the protein tracer (125I), demonstrating selective CE uptake from LpA-I as well as from LpA-I:A-II. This difference in uptake between [3H]CEt and 125I, i.e. the rate of apparent selective CE uptake, was significantly higher for LpA-I compared to LpA-I:A-II, and this was dose- as well as time-dependent. Thus in human hepatic cell and fibroblasts, CE are selectively taken up to a higher extent from LpA-I compared to LpA-I:A-II. These results may suggest that LpA-I particles of the human plasma HDL fraction may be those lipoproteins which more efficiently deliver CE to the liver via the selective uptake pathway whereas LpA-I:A-II may play a less important role.
高密度脂蛋白（HDL）相关胆固醇酯（CE）的选择性摄取，即不依赖HDL颗粒摄取的脂质摄取，在体内和体外均可将CE输送至肝脏和类固醇生成组织。从人血浆HDL中可分离出两种主要的颗粒亚群：一种同时含有载脂蛋白（apo）A-I和apo A-II（称为LpA-I:A-II）作为主要蛋白质成分，而另一种则不含apo A-II（LpA-I）。在本研究中，对培养细胞从LpA-I和LpA-I:A-II中选择性摄取CE的情况进行了研究。通过免疫亲和色谱法从人血浆高密度脂蛋白3（HDL3，d = 1.125 - 1.21 g/ml）中分离出LpA-I和LpA-I:A-II，两种颗粒的蛋白质（125I）以及CE部分（[3H]胆固醇油醚（[3H]CEt））均被放射性标记。多项对照实验验证了所采用的标记方法。为研究CE的选择性摄取，将人Hep G2肝癌细胞、原代培养的人肝细胞和人皮肤成纤维细胞在含有双重放射性标记的LpA-I或LpA-I:A-II颗粒的培养基中孵育。此后测定细胞示踪剂含量。对于每种细胞类型，根据脂质示踪剂（[3H]CEt）计算的表观脂蛋白颗粒摄取速率大大超过了蛋白质示踪剂（125I）所致的摄取速率，表明从LpA-I以及LpA-I:A-II中均可选择性摄取CE。与LpA-I:A-II相比，LpA-I的[3H]CEt和125I摄取差异，即表观选择性CE摄取速率显著更高，且呈剂量和时间依赖性。因此，在人肝细胞和成纤维细胞中，与LpA-I:A-II相比，从LpA-I中选择性摄取CE的程度更高。这些结果可能表明，人血浆HDL组分中的LpA-I颗粒可能是那些通过选择性摄取途径更有效地将CE输送至肝脏的脂蛋白，而LpA-I:A-II可能起的作用较小。
