Hoekstra D, Tomasini R, Scherphof G
Biochim Biophys Acta. 1978 Sep 6;542(3):456-69. doi: 10.1016/0304-4165(78)90376-8.
We studied the interaction of positively and negatively charged unilamellar and multilamellar phospholipid vesicles (liposomes) with rat-liver parenchymal cells in primary monolayer culture. Radioactive liposomal phosphatidylcholine was taken up more rapidly and to a larger extent from unilamellar than from multilamellar vesicles. No significant difference in uptake characteristics was observed between vesicles of different charge. The presence of serum greatly reduced uptake of liposomal phosphatidylcholine of both unilamellar and multilamellar vesicles. This serum effect was independent of surface charge of the vesicles. When cells were allowed to take up radioactive liposomal phospholipid and then incubated further in absence of vesicles, part of the radioactivity associated with the cells was released into the medium, most of it as water soluble degradation products. When cells were preincubated with vesicles containing horseradish peroxidase and then, after removal of the vesicles, further incubated, peroxidase activity could be demonstrated in the culture medium, part of it only after addition of Triton X-100. These observations were taken to indicate that part of the phospholipid taken up the cells represented vesicles binding to the cell surface rather than having been internalized. Vesicle-entrapped [125I]albumin was taken up by the cells and rapidly hydrolyzed as indicated by the appearance of radioactivity soluble in trichloroacetic acid within minutes after starting the incubation. No uptake of free albumin could be demonstrated. The kinetics of albumin uptake and release of trichloroacetic acid-soluble radioactivity from the cells suggest that, initially, liposomes are internalized predominantly by endocytosis, while during prolonged incubation fusion of the liposomal membrane with the plasma membrane gradually contributes more substantially to the overall uptake process. The significance of these findings is emphasized with special reference to the use of liposomes as intravenous carriers of enzymes or drugs.
我们研究了带正电荷和负电荷的单层和多层磷脂囊泡（脂质体）与原代单层培养的大鼠肝实质细胞之间的相互作用。放射性脂质体磷脂酰胆碱从单层囊泡中的摄取速度更快，摄取量也比多层囊泡更大。不同电荷的囊泡在摄取特性上未观察到显著差异。血清的存在大大降低了单层和多层囊泡中脂质体磷脂酰胆碱的摄取。这种血清效应与囊泡的表面电荷无关。当细胞摄取放射性脂质体磷脂后，在无囊泡的情况下进一步孵育，与细胞相关的部分放射性会释放到培养基中，大部分以水溶性降解产物的形式存在。当细胞与含有辣根过氧化物酶的囊泡预孵育，然后在去除囊泡后进一步孵育时，培养基中可检测到过氧化物酶活性，部分活性仅在添加 Triton X - 100 后出现。这些观察结果表明，细胞摄取的部分磷脂代表与细胞表面结合的囊泡，而非内化的囊泡。囊泡包裹的[125I]白蛋白被细胞摄取并迅速水解，孵育开始几分钟后，三氯乙酸可溶性放射性的出现表明了这一点。未检测到游离白蛋白的摄取。白蛋白摄取动力学以及细胞中三氯乙酸可溶性放射性的释放表明，最初，脂质体主要通过内吞作用内化，而在长时间孵育过程中，脂质体膜与质膜的融合对整体摄取过程的贡献逐渐增大。特别参考脂质体作为酶或药物的静脉载体的应用，强调了这些发现的重要性。
