Development of Medically ApplicableLiposomes as Enzyme or Drug Carriers

小鼠静脉注射含蔗糖酶的负单分子脂质体(PC/Chol/DCP，摩尔比4：5：1)，以脂双层中的(~(14)C&gt；)三棕榈素为标志物，观察其对肝脏的掺入情况。脂质体在肝脏的摄取速度在注射后1小时达到最大值，然后逐渐下降，通过(&lt；^(14)C&gt；)三棕榈素的放射性检测。另一方面，肝脏中的转氨酶活性在2小时内逐渐增加，并在此后的15小时内保持不变。小鼠肝脏的亚细胞分级显示，脂质体具放射性的脂类放射性和富含溶酶体组分中的转化酶活性占主导地位。含有放射性三棕榈素的脂质体被认为通过内吞作用被肝脏摄取，然后被输送到溶酶体中。放射性三棕榈素在脂质体中的肝内去向表明，它们被溶酶体脂肪酶迅速降解为游离脂肪酸，并被重新用于内质网中磷脂的合成。含有有效的溶酶体酶抑制剂E-的脂质体可通过脂质体保护注射酶在溶酶体内的降解。乳糖神经酰胺(LacCer)或去唾液酸叶绿素糖链(AFSC)在DMPC或DPPC脂质体中加入这些标志物时，可诱导脂质体在肝脏中的摄取增加，而在鸡蛋PC脂质体中则不能。这表明脂质体膜流动性参与了肝脏的摄取。虽然LacCer或AFSC对分离的Kupffer细胞无效，但它们增加了脂质体在分离的实质细胞中的摄取。LacCer的这种增强作用被AF的加入所消除，这表明有证据表明存在半乳糖特异性受体药物内吞作用。

The incorporation into liver of the negative unilameller liposomes (PC/Chol/DCP, molar ratio 4:5:1) containing invertase in the aqueous compartment and ( <^(14)C> )tripalmitin in the lipid bilayer as marker was examined after intravenous injection into mouse. The rate of uptake by the liver of the liposomes reached a maximum liver 1 hr after injection and then gradually declined as examined by radioactivity of ( <^(14)C> )tripalmitin. On the other hand, the invertase activity in the liver was gradually increased up to 2 hr and remained fairly constant during 15 hr thereafter. Subcellular fractionation of the mouse liver loaded with the liposomes showed a predominant localization of liposomal lipid radioactivity and invertase activity in the lysosome-rich fraction. Liposomes with radioactive tripalmitins are considered to be taken up by liver via endocytosis and subsequently delivered into lysosomes. The intrahepatic fate of the radioactive tripalmitin in liposomes indicated that they were rapidly degraded by lysosomal lipase to free fatty acids, which were reutilized for synthesis of phospholipids in endoplasmic reticulum. The administration of the liposomes containing E-64, a potent lysosomal protease inhibitor, was able to protect the intralysosomal degradation of the injected enzymes via liposomes.Lactosylceramide (LacCer) or asialofetuin sugar chain (AFSC) induced an increment of the liposomal uptake into the liver when these markers were incorporated in DMPC or DPPC-based but not in eggPC liposomes. This suggested an involvement of liposomal membrane fluidity in the liver uptake. LacCer or AFSC increased liposomal uptake in the isolated parenchymal cells, although they were ineffective for isolated Kupffer cells. Such enhancing effect of LacCer was abolished by the addition of AF, suggesting evidence for a galactose-specific receptormedicated endocytosis.