Increased affinity of liposomes derived from total spleen and liver lipids to spleen cells

The interaction of liposomes derived from total lipids of mouse spleen and liver with mouse spleen cells was studied. It was shown that the binding of these liposomes is much higher than the binding of liposomes obtained from a model lipid mixture--phosphatidylcholine--phosphatidylethanolamine--cholesterol (2:1:1). Adherent and nonadherent spleen cells were found to have affinity for liposomes derived from total lipids of spleen or liver. Removal of gangliosides and protein contaminants from the liposomes derived from total spleen lipids caused an increased binding of liposomes to spleen cells. Multilamellar liposomes bound more effectively to ultrasonicated vesicles having a homologous lipid composition than the liposomes with a different lipid composition. The increased affinity of liposomes derived from total lipids of spleen or liver for spleen cells may account for the identical fluidity of the lipid bilayer of liposomes and plasma membranes of spleen cells.     

Large liposomes containing ganglioside GM1 accumulate effectively in spleen

Large liposomes, with a composition of egg phosphatidylcholine, cholesterol and ganglioside GM1, prepared by an extrusion method, were injected intravenously into mice. After 24 h, up to 50% of injected dose was accumulated in spleen compared with about 15% in spleen for liposomes containing no GM1. The effect of GM1 on spleen accumulation of liposomes was liposome size dependent. Only relatively large liposomes (d greater than 300 nm) showed high accumulation; smaller liposomes were progressively less accumulated. The spleen accumulation increased with increasing injection dose of the liposomes. It was noted that the enhanced uptake by spleen was accompanied by a decrease in the liver uptake, but the total uptake of liposomes by liver and spleen was not dependent on the diameter of liposome or the presence of the ganglioside GM1. Autoradiographs of fixed and sectioned spleen using 125I-labeled tyraminylinulin as a content marker for the liposomes, showed that liposomes localized at the reticular meshwork of the red pulp. These results suggest that larger liposomes containing GM1 are filtered by the spleen during the circulation in blood. The smaller ones with a mean diameter of less than 100 nm are not retained by the filter. The function of GM1 is to prevent liposomes from a rapid uptake by the liver so that liposomes may circulate through the spleen and be filtered. These results, together with the observation that the liposome-entrapped proteins were degraded by the spleen, suggest the potential use of these liposomes for specific drug delivery to the spleen.     

Tissue distribution of EDTA encapsulated within liposomes containing glycolipids or brain phospholipids

Multilamellar liposomes were prepared with various asialoglycolipids, gangliosides, sialic acid, or brain phospholipids in the liposome membrane and with ethylenediaminetetraacetic acid (EDTA) encapsulated in the aqueous compartments. The liposomes containing glycolipids or sialic acid were prepared from a mixture of phosphatidylcholine, cholesterol, and one of the following test substances: galactocerebroside, glucocerebroside, galactocerebroside sulfate, mixed gangliosides, monosialoganglioside G_M1, monosialoganglioside G_M2, monosialoganglioside G_M3, disialoganglioside G_D1a, or sialic acid. The liposomes containing brain phospholipids were mixtures of either sphingomyelin and cholesterol or a brain total phospholipid extract and cholesterol. Distribution of ¹⁴C-labeled EDTA were determined in mouse tissues from 15 min to 6 h or 12 h after a single injection of liposome prepartion. Liver uptake of encapsulated EDTA was lowest from all liposome preparations containing sialic acid or sialogangliosides regardless of the amount of sialic acid moiety present or the identity of the particular ganglioside; highest uptake of encapsulated EDTA by liver was from the liposomes containing galactocerebroside or brain phospholipids. Lungs and brain took up the largest amounts of EDTA from liposomes containing sphingomyelin and lesser amounts from liposomes containing G_D1a. Use of mouse brain phospholipid extract to prepare liposomes did not increase uptake of encapsulated EDTA by the brain. EDTA in liposomes containing monosialogangliosides, brain phospholipids, galactocerebroside, or sialic acid was taken up well by spleen and marrow. Highest thymus uptake of encapsulated EDTA was from liposomes containing G_D1a. These results demonstrate that inclusion of sialogangliosides in liposome membranes decreases uptake of liposomes by liver, thus making direction of encapsulated drugs to other organs more feasible. Liposomes containing glycolipids also have potential uses as probes of cell surface receptors.     

Effect of the lipid composition of liposomes on their clearance from the circulation and accumulation in the liver of mice

The effect of phospholipid and ganglioside liposome composition on the liposome clearance from the circulation and accumulation in the mouse liver has been studied. It has been shown that liposomes constituting of liver lipids are quicker removed from the circulation and accumulated in the liver. Liver gangliosides increased liposome uptake by the mouse liver and their clearance from the circulation.     

Effect of Macrophage Elimination Using Liposome-Encapsulated Dichloromethylene Diphosphonate on Tissue Distribution of Liposomes

Abstract

Effect of macrophage elimination using liposomal dichloromethylene diphosphonate (C1₂MDP)1 on tissue distribution of different types of liposomes was examined in mice. Intravenously administration into mice with CI2MDP encapsulated in liposomes composed of phosphatidylcholine, cholesterol and phosphatidylserine exhibits a temporary blockade of liver and spleen function for liposome uptake. At a low dose of 90 (ig/mouse, the liposome uptake by the liver was significantly decreased. Such decrease was accompanied by an increase in liposome accumulation in either spleen or blood depending on liposome composition and size. Direct correlation between the administration dose of liposomal CI2MDP and the liposome circulation time in blood was also obtained even for liposomes with an average diameter of more than 500 nm. These results indicate that temporary elimination of macrophages of the liver and spleen using liposomal CI2MDP may prove to be useful to enhance the drug delivery efficiency of liposomes.     

Tissue distribution of EDTA encapsulated within liposomes of varying surface properties

Liposomes containing ethylenediaminetetraacetic acid (EDTA) were prepared with different surface properties by varying the liposomal lipid constituents. Positively charged liposomes were prepared with a mixture of phosphatidylcholine, cholesterol, and stearylamine. Negatively charged liposomes were prepared with a mixture of phosphatidylcholine, cholesterol, and phosphatidylserine. Neutral liposomes were prepared with phosphatidylcholine alone, dipalmitoyl phosphatidylcholine alone, or with a mixture of phosphatidylcholine and cholesterol. Distributions of ¹⁴C-labeled EDTA were determined in mouse tissues from 5 min to 24 h after a single intravenous injection of liposome preparation. Differences in tissue distribution were produced by the different liposomal lipid compositions. Uptake of EDTA by spleen and marrow was highest from negatively charged liposomes. Uptake of EDTA by lungs was highest from positively charged liposomes; lungs and brain retained relatively high levels of EDTA from these liposomes between 1 and 6 h after injection. Liver uptake of EDTA from positively or negatively charged liposomes was similar; the highest EDTA uptake by liver was from the neutral liposomes composed of a mixture of phosphatidylcholine and cholesterol. Liposomes composed of dipalmitoyl phosphatidylcholine produced the lowest liposomal EDTA uptake observed in liver and marrow but modrate uptake by lungs. Tissue uptake and retention of EDTA from all of the liposome preparations were greater than those of non-encapsulated EDTA. The results presented demonstrate that the tissue distribution of a molecule can be modified by encapsulation of that substance into liposomes of different surface properties. Selective delivery of liposome-encapsulated drugs to specific tissues could be effectively used in chemotherapy and membrane biochemistry.     

Tissue distribution of EDTA encapsulated within liposomes containing glycolipids or brain phospholipids.

Multilameller liposomes were prepared with various asialoglycolipids, gangliosides, sialic acid, or brain phospholipids in the liposome membrane and with ethylenediaminetetraacetic acid (EDTA) encapsulated in the aqueous compartments. The liposomes containing glycolipids or sialic acid were prepared from a mixture of phosphatidylcholine, cholesterol, and one of the following test substances: galactocerebroside, glucocerebroside, galactocerebroside sulfate, mixed gangliosides, monosialoganglioside GM1, monosialoganglioside GM2, monosialoganglioside GM3, disialoganglioside GD1a, or sialic acid. The liposomes containing brain phospholipids were mixtures of either sphingomyelin and cholesterol or a brain total phospholipid extract and cholesterol. Distributions of 14C-labeled EDTA were determined in mouse tissues from 15 min to 6 h or 12 h after a single injection of liposome preparation. Liver uptake up encapsulated EDTA was lowest from all liposome preparations containing sialic acid or sialogangliosides, regardless of the amount of sialic acid moiety present or the identity of the particular ganglioside; highest uptake of encapsulated EDTA by liver was from liposomes containing galactocerebroside or brain phospholipids. Lungs and brain took up the largest amounts of EDTA from liposomes containing sphingomyelin and lesser amounts from liposomes containing GD1a. Use of mouse brain phospholipid extract to prepare liposomes did not increase uptake of encapsulated EDTA by the brain. EDTA in liposomes containing monosialogangliosides, brain phospholipids, galactocerebroside, or sialic acid was taken up well by spleen and marrow. Highest thymus uptake of encapsulated EDTA was from liposomes containing GD1a. These results demonstrate that inclusion of sialogangliosides in liposome membranes decreases uptake of liposomes by liver, thus making direction of encapsulated drugs to other organs more feasible. Liposomes containing glycolipids also have potential uses as probes of cell surface receptors.     

Depletion and repopulation of macrophages in spleen and liver of rat after intravenous treatment with liposome-encapsulated dichloromethylene diphosphonate

Summary Rats received a single intravenous injection with liposome-encapsulated dichloromethylene diphosphonate (Cl2MDP). This treatment resulted in the elimination of macrophages in spleen and liver within 2 days. Macrophages ingest the liposomes and are destroyed by the drug, which is released from the liposomes after disruption of the phospholipid bilayers under the influence of lysosomal phospholipases. Repopulation of macrophages in spleen and liver was studied at different time intervals after treatment. Macrophages in the liver (Kupffer cells) and red pulp macrophages in the spleen were the first cells to reappear, followed by marginal metallophilic macrophages and marginal-zone macrophages in the spleen. Different markers of the same cell did not reappear simultaneously. On the other hand, the same marker (recognized by the monoclonal antibody ED2) reappeared much more rapidly in the liver than in the spleen. The present results in the rat were different from those earlier obtained in the mouse. Red pulp macrophages were the first cells and marginal zone macrophages were the last cells to repopulate the spleen in both rodents after treatment with Cl2MDP liposomes. However, there was much more overlap in the repopulation kinetics of splenic macrophage subpopulations in the rat, when compared with the mouse.     

Distribution of [3H]cholesterol-labelled liposomes with or without praziquantel in mice infected with Mesocestoides corti (Cestoda) tetrathyridia

The anthelmintic drug praziquantel (PZQ) has a short half-life in the circulation, necessitating repeated daily administration of PZQ for the therapy of larval stages of cestodes. The effect of incorporation of PZQ into multilamellar liposomes on their biodistribution in Mesocestoides corti (syn. M. vogae) infected mice has been examined using [3H]cholesterol as a liposomal marker. Incorporation of PZQ significantly increased the average size of liposomes with 70.3% of [3H]lip.PZQ particles up to 1.9 microm, whereas higher portion of [3H]liposomes (66.3% of total) were of smaller (up to 1.3 microm). Both liposome preparations were given intraperitoneally to avoid rapid sequestration in the liver. There were significant differences between [3H]liposomes and [3H]lip.PZQ-associated radioactivity in peritoneal adherent cells, liver- and peritoneal larvae, liver, spleen and lymph nodes within 16 days of examination. The highest uptake (about 2-fold more [3H]lip.PZQ than [3H]liposomes from the total dose) was found in peritoneal cells on day 1 post therapy (p.t.) followed by a rapid decline. The kinetic of decline in these cells recovered on day 1 p.t. was studied also in vitro. Disappearance of the marker due to the breakdown of liposomes and efflux of lipids and PZQ from cells was slower for [3H]lip.PZQ in comparison with drug-free liposomes and was not completed after 4 days-incubation. Significantly increased levels of radioactivity, more in [3H]liposomes treated groups, were recorded in the liver- and peritoneal larvae between days 8-16 p.t. indicating re-utilization of cholesterol by the larvae. The data suggest that incorporation of PZQ into liposomes contributes to the enlargement of liposome average size and slows down their degradation in phagocytosing cells. In this respect, these cells could serve as the secondary circulating depots for PZQ releasing it slowly to the circulation.     

Effect of cholesterol on the uptake and intracellular degradation of liposomes by liver and spleen; a combined biochemical and gamma-ray perturbed angular correlation study

We investigated the effect of cholesterol on the uptake and intracellular degradation of liposomes by rat liver and spleen macrophages. Multilamellar vesicles (MLV) consisting of distearoylphosphatidylcholine/phosphatidylserine (molar ratio 9:1) or distearoylphosphatidylcholine/cholesterol/phosphatidylserine (molar ratio 4:5:1) were labeled with [3H]cholesteryl hexadecyl ether and/or cholesteryl [14C]oleate. After i.v. injection the cholesterol-containing liposomes were eliminated less rapidly from the bloodstream and taken up to a lesser extent by the liver (macrophages) than the cholesterol-free liposomes. Assessment of the 3H/14C ratios in liver and spleen cells revealed that the cholesterol-containing liposomes are substantially more resistant towards intracellular degradation than the cholesterol-free liposomes. These results could be confirmed by measuring the release of 111In from liposomes after uptake by liver and spleen by means of gamma-ray perturbed angular correlation spectroscopy. Experiments with cultured Kupffer cells in monolayer also revealed that incorporation of cholesterol results in a decrease of the uptake and an increase of the intracellular stability of cholesteryl [14C]oleate-labeled liposomes. Finally, incubation of both types of liposomes with lysosomal fractions prepared from rat liver demonstrated a difference in susceptibility to lysosomal degradation: the cholesterol-free vesicles were much more sensitive to lysosomal esterase than the cholesterol-containing liposomes. These results may be relevant to the application of liposomes as a drug carrier system to liver and spleen (macrophages).     

Intrahepatic distribution of small unilamellar liposomes as a function of liposomal lipid composition

We investigated the intrahepatic distribution of small unilamellar liposomes injected intravenously into rats at a dose of 0.10 mmol of lipid per kg body weight. Sonicated liposomes consisting of cholesterol/sphingomyelin (1:1), (A); cholesterol/egg phosphatidylcholine (1:1), (B); cholesterol/sphingomyelin/phosphatidylserine (5:4:1), (C) or cholesterol/egg-phosphatidylcholine/phosphatidylserine (5:4:1), (D) were labeled by encapsulation of [3H]inulin. The observed differences in rate of blood elimination and hepatic accumulation (A much less than B approximately equal to C less than D) confirmed earlier observations and reflected the rates of uptake of the four liposome formulations by isolated liver macrophages in monolayer culture. Fractionation of the liver into a parenchymal and a non-parenchymal cell fraction revealed that 80-90% of the slowly clearing type-A liposomes were taken up by the parenchymal cells while of the more rapidly eliminated type-B liposomes even more than 95% was associated with the parenchymal cells. Incorporation of phosphatidylserine into the sphingomyelin-based liposomes caused a significant increase in hepatocyte uptake but a much more substantial increase in non-parenchymal cell uptake, resulting in a major shift of the intrahepatic distribution towards the non-parenchymal cell fraction. For the phosphatidylcholine-based liposomes incorporation of phosphatidylserine did not increase the already high uptake by the parenchymal cells while uptake by the non-parenchymal cells was only moderately elevated; this resulted in only a small shift in distribution towards the non-parenchymal cells. The phosphatidylserine-induced increase in liposome uptake by non-parenchymal liver cells was paralleled by an increase in uptake by the spleen. Fractionation of the non-parenchymal liver cells in a Kupffer cell fraction and an endothelial cell fraction showed that even for the slowly eliminated liposomes of type A endothelial cells do not participate to a measurable extent in the elimination process, thus excluding involvement of fluid-phase pinocytosis in the uptake process.     

转铁蛋白修饰脂质体的制备及其肝癌靶向性研究

目的：肿瘤的靶向治疗是当前研究的热点,肝肿瘤细胞表面有大量的转铁蛋白受体表达,而正常组织较少,因此本研究制备转铁蛋白（TF）修饰的脂质体（TFLPs）,并对其肝肿瘤靶向性进行研究。方法：采用薄膜分散法制备普通脂质体,考察其形态,粒径,电位。通过体外血清稳定性模拟脂质体进入体内后的稳定性。通过HepG2肿瘤细胞对TFLPs的摄取实验考查脂质体与肝癌细胞的亲和力。构建荷瘤裸鼠模型,考查TFLPs在荷瘤裸鼠体内的分布。结果：所制备的TFLPs平均粒径为108．8±9．5nm,Zeta电位为．1．80±0．73mV。学期稳定性试验结果显示,TFLPs在24h内具有良好的血清稳定性。体外细胞摄取实验表明,HepG2细胞对TFLPs的摄取效率是普通长循环脂质体（LPs）的3．4倍。荷瘤裸鼠肝组织和肿瘤组织切片结果显示,TFLPs比LPs具有更好的肿瘤靶向性。结论：该脂质体制备方法简单,与LPs相比,经转铁蛋白修饰可显著提高肿瘤细胞对脂质体的摄取,TFLPs是一种潜在高效的肝癌靶向给药系统。     

Uptake and processing of immunoglobulin-coated liposomes by subpopulations of rat liver macrophages

In vivo uptake and processing by liver macrophages (Kupffer cells) of liposomes, covalently coated with rabbit immunoglobulin (Ig liposomes) was studied following intravenous injection in rats. Rabbit Ig liposomes were labeled with trace amounts of cholesteryl[14C]oleate and [3H]cholesteryl hexadecyl ether. 1 h after injection of the liposomes, the non-parenchymal cells were isolated and subjected to centrifugal elutriation with stepwise-increasing flow rates; thus, five sub-fractions of Kupffer cells were obtained ranging in size from 9 to 14 micron in diameter. The cells were assayed for peroxidase activity and protein content. Rabbit Ig liposomes were taken up preferentially by Kupffer cells with diameters larger than 11 micron, which constitute less than 25% of the total Kupffer cell population. The intralysosomal degradation of the ingested liposomes was monitored by measuring the 3H/14C ratio of the cells. Due to the rapid release from the cells of the [14C]oleate formed from the cholesteryl[14C]oleate and the virtually complete retention of the non-metabolizable [3H]cholesteryl hexadecyl ether the 3H/14C ratio of the cells increases with proceeding hydrolysis of the liposomes. Thus, we were able to show that, in vivo, the Kupffer cells of the larger size classes, are not only more active in liposome uptake, but are also substantially more active in liposome degradation than smaller cells. The maintenance of the observed heterogeneity of rat liver Kupffer cells, with respect to liposome uptake under in vitro culture conditions, was examined. Subfractions were maintained in monolayer culture for 2 days and incubated with rabbit Ig liposomes. Binding and uptake of liposomes by the cells was monitored by measuring cell-associated radioactivity at 4 degrees C and 37 degrees C, respectively. In contrast to our in vivo results, we observed maximal in vitro liposome binding and uptake in those subfractions containing small cells (10-11 micron diameter), while the fractions containing cells larger than 12 micron, which were more active in vivo, were substantially less active than the smaller cells. The maximum we observed was even more pronounced when the liposome concentration was increased. We conclude that liver macrophage subfractions that barely participate in liposome uptake from the bloodstream in vivo, possess the potential to develop the capacity in vitro to phagocytose rabbit Ig-coated liposomes to extents equal to or even higher than the cells belonging to those subfractions containing the phagocytically most active cells under in vivo conditions.     

Enzyme replacement with liposomes containing beta-galactosidase from Charonia lumpas in murine globoid cell leukodystrophy (twitcher)

Enzyme replacement with liposomes containing beta-galactosidase obtained from charonia lumpas was carried out in murine globoid cell leukodystrophy (GLD). Charonia lumpas beta-galactosidase was able to hydrolyze galactocerebroside trapped into liposomes prepared from lecithin, cholesterol and sulfatide (molar ratio; 7:2:1). Liposomes containing charonia lumpas beta-galactosidase were successfully incorporated into the mouse tissues. 3H-galactocerebroside labeled liposomes were also incorporated into mouse liver, spleen and other tissues. The accumulation rate of 3H-galactocerebroside into twithcer mice liver and spleen was almost 40 to 100 times higher than those of controls and degraded to 70 to 80% of accumulated radioactivity of 3H-galactocerebroside by single injection of liposomes containing charonia lumpas beta-galactosidase. Results suggest that exogeneous enzyme trapped in liposomes can be useful for the correction of accumulated compound.     

Grafting of different glycosides on the surface of liposomes and its effect on the tissue distribution of 125I-labelled γ-globulin encapsulated in liposomes

Different glycosides were grafted on the surface of liposomes containing ¹²⁵I-labelled γ-globulin by two ways: (1) by using glycolipid and (2) by covalent coupling of $\text{p-}\text{aminophenyl-}\text{d}\text{-glycosides}$ to phosphatidylethanolamine liposomes using glutaraldehyde. The distribution of ¹²⁵I-labelled γ-globulin was determined in mouse tissues from 5–60 min after a single injection of these liposomes. The liver uptake of encapsulated ¹²⁵I-labelled γ-globulin was highest from liposomes having galactose and mannose on the surface. Competition experiments and cross-inhibition studies indicate that this uptake are mediated by specific recognition of the surface galactose and mannose residues of liposomes by the receptors present on the plasma membrane of liver cells. Stearylamine-containing liposomes were found to be more efficient in mediating the uptake of ¹²⁵I-labelled γ-globulin by the lung, whereas in the case of spleen, phosphatidylethanolamine liposomes were more efficient. The extent of uptake of ¹²⁵I-labelled γ-globulin from all types of liposome decreases as the amount of given liposomes increases. The uptake of ¹²⁵I-labelled γ-globulin from liposomes containing asialogangliosides depends upon the phospholipid/ glycolipid ratio. These experiments clearly demonstrate that enhanced liposome uptake by liver cells could be achieved by grafting galactose and mannose on the liposomal surface.     

Enhancement of immune responses by DNA vaccination through targeted gene delivery using mannosylated cationic liposome formulations following intravenous administration in mice

The present study investigated the potency of the mannosylated cationic liposomes (Man liposomes) that we have developed in novel DNA vaccine carrier. Ovalbumin (OVA) was selected as a model antigen for vaccination; accordingly, OVA-encoding pDNA (pCMV-OVA) was constructed to evaluate DNA vaccination. The potency of the Man liposome/pCMV-OVA complex was compared with naked pCMV-OVA and that complexed with DC-Chol liposomes. In cultured mouse peritoneal macrophages, MHC class I-restricted antigen presentation of the Man liposome/pCMV-OVA complex was significantly higher than that of naked pCMV-OVA and that complexed with DC-Chol liposomes. After intravenous administration, OVA mRNA expression and MHC class I-restricted antigen presentation on CD11c+ cells and inflammatory cytokines, such as TNF-alpha, IL-12, and IFN-gamma, that can enhance the Th1 response of the Man liposome/pCMV-OVA complex were higher than that of naked pCMV-OVA and that complexed with DC-Chol liposomes. Also, the spleen cells from mice immunized by intravenous administration of the Man liposome/pCMV-OVA complex showed the highest proliferation response and IFN-gamma secretion. These findings suggest that the targeted delivery of DNA vaccine by Man liposomes is a potent vaccination method for DNA vaccine therapy.     

Enveloped viruses as model membrane systems: microviscosity of vesicular stomatitis virus and host cell membranes.

The fluorescence probe 1,6-diphenyl-1,3,5-hexatriene was used to study and compare the dynamic properties of the hydrophobic region of vesicular stomatitis virus grown on L-929 cells, plasma membrane of L-929 cells prepared by two different methods, liposomes prepared from virus lipids and plasma membrane lipids, and intact L-929 cells. The rate of penetration of the probe into the hydrophobic region of the lipid bilayer was found to be much faster in the lipid vesicle bilayer as compared with the intact membrane, but in all cases the fluorescence anisotropy was constant with time. The L-cell plasma membranes, the vesicles prepared from the lipids derived from the plasma membranes, and intact cells are found to have much lower microviscosity values than the virus or virus lipid vesicles throughout a wide range of temperatures. The microviscosity of plasma membrane and plasma membrane lipid vesicles was found to depend on the procedure for plasma membrane preparation as the membranes prepared by different methods had different microviscosities. The intact virus and liposomes prepared from the virus lipids were found to have very similar microviscosity values. Plasma membrane and liposomes prepared from plasma membrane lipids also had similar microviscosity values. Factors affecting microviscosity in natural membranes and artificially mixed lipid membranes are discussed.     

Incorporation of mannose 6-phosphate receptors into liposomes. Receptor topography and binding of alpha-mannosidase.

A receptor that binds the lysosomal enzyme alpha-mannosidase via mannose 6-phosphate moieties (mannose 6-phosphate receptor) was purified from Swarm-rat chondrosarcoma and bovine liver microsomal membranes. Receptor-reconstituted liposomes were prepared by dialysis of taurodeoxycholate-dispersed lipids with purified mannose 6-phosphate receptor. Liposomes appeared by electron microscopy as 60-120 nm unilamellar vesicles. Receptor-reconstituted liposomes retained the ability to bind alpha-mannosidase specifically. Binding was saturable with an apparent Kd of 1 nM and was competitively inhibited by mannose 6-phosphate (Ki 2mM). Liposomes containing entrapped 125I-bovine serum albumin were used to demonstrate that treatment with 0.045% taurodeoxycholate rendered liposomes permeable to macromolecules without solubilizing the membrane. Receptor orientation in the liposome membrane was established by measuring binding of ligand to intact and detergent-treated liposomes. Unlike coated vesicles, which contain cryptic mannose 6-phosphate receptors [Campbell, Fine, Squicciarini & Rome (1983) J. Biol. Chem. 258, 2526-2533], treatment of liposomes with detergent revealed no additional cryptic binding sites. In addition, treatment of liposomes with 0.75% trypsin abolished total receptor binding activity. The results suggest that the receptor is inserted with its binding site facing the outside of the liposome.     

靶向树突状细胞表面分子DEC-205长循环免疫脂质体稳定性模型的构建及其生物学特性

应用多相分散体系的动力稳定性和聚结稳定性理论,以薄膜分散法构建了靶向树突状细胞（dendritic cells,DCs）表面分子DEC-205长循环免疫脂质体（anti—DEC-205 iLPSM）的稳定性模型,并对其物理稳定性、生物学特性等进行了考察。结果表明经优化后的脂质体4℃贮存7d后粒径分布变化较小;FTTC-dextran累积泄漏率小于7％;耦联抗DEC-205的免疫脂质体（anti—DEC-205 iLPSM）可特异性地识别DCs,并作为良好载体将FITC-dextran带入DCs浆内。anti—DEC-205 iLPSM模型的构建为进一步研究抗原靶向DEC-205受体后的体内免疫应答情况提供了工作基础,有望开发一种新型DCs疫苗应用于临床。     

Pharmacokinetics of the iron chelator desperrioxamine as affected by liposome encapsulation: potential in treatment of chronic hemosiderosis

Desferrioxamine (DF), the chelator of choice for removal of excess stored iron, is limited by its rapid excretion, metabolic breakdown, and low cell uptake. We have encapsulated DF in unilamellar and multilamellar liposomes, and have compared the short-term pharmacokinetics of nonencapsulated and encapsulated ⁵⁹Fe-labeled DF after intravenous administration. Disappearance of ⁵⁹Fe-DF from the plasma was very rapid in mice receiving multilamellar liposome-encapsulated and nonencapsulated drug, but much slower in mice receiving unilamellar liposomes. Between 1 and 24 hours after injection, nonencapsulated ⁵⁹Fe-DF never exceeded 1–5% of the injected dose (ID) in liver or < 0.7% in spleen; whereas after either multilamellar or unilamellar liposomes, the uptake in liver was 30–35% ID, and in spleen was 1–5% ID. Excretion of ⁵⁹Fe-DF was much slower with liposome encapsulation. These results indicate that liposomes can effectively deliver DF to critical organs of iron storage. Thus this drug delivery system is potentially useful for treatment of iron overload.