Nebulization of Liposomes. I. Effects of Lipid Composition

A series of multilamellar liposome dispersions was prepared from lipids of soy phosphatidylcholine or hydrogenated soy phosphatidylcholine containing from 0 to 30 mol% of either cholesterol, steary-lamine, or dipalmitoyl phosphatidylglycerol. The liposome dispersions were aerosolized with a Collison nebulizer for 80 min at an output flow rate of 4.7 liters of air/min. The effects of nebulization on the vesicles were determined by monitoring the release of encapsulated 5,6-carboxyfluorescein (CF) from dispersions containing 200 µg of total CF, of which 93.1 ± 2.4% (N = 18) was initially encapsulated. In all experiments CF was released from the liposomes while being aerosolized, and this ranged from a mean of 12.7 ± 3.8 to 60.9 ± 1.9% of the encapsulated CF, depending upon the lipid composition. The lipid concentration in the dispersions did not affect the rate or percentage release of CF over a range of 0.5 to 50 mg per nebulized dispersion. If liposomes are to be used as drug carriers in an inhalation aerosol a lipid composition should be employed which will minimize the release of encapsulated drug caused by nebulization.     

Molecular approach to the nucleo-melanosomal interaction in human melanoma cells

This paper presents evidence that L-tyrosine oxidation products and 5,6-dihydroxyindole, an intermediate of melanin synthesis bind to and modify DNA structure, as tested by extracting cell DNA, using topoisomerase I and denaturation assays. When supercoiled plasmid pCU18 or pBR322 DNAs are treated with 5,6-dihydroxyindole the supercoiled species disappear and are converted to species less mobile in a gel retardation test with respect to relaxed DNA. 5,6-Dihydroxyindole causes an easier acid denaturation of the double helix. The results, that are dose dependent,would point to both intercalation and cross-linking of DNA by 5,6-dihydroxyindole and its oxidation product(s). ³H-L-tyrosine deriving radioactivity, bound to nuclear DNA, is higher at low pH, (5.6) if compared to pH 6.8. The highest radioactivity bound to cell DNA is found during the transition from the amelanotic to the melanotic phenotype in human melanoma cell lines. As a control, the binding of ³H-L-tyrosine radioactivity to human prostate fibroblast DNA was investigated.     

Response of multicellular tumor spheroids to liposomes containing TNF-α

Summary This publication describes a new model to investigate the influence of tumor necrosis factor- (TNF-) on a three-dimensional glial cell aggregate under defined, standardized, reproducible conditions using the glioma cell line A 172.The cells are initially grown as normal monolayer culture until they reach a cell density of up to 1×10⁶. Subsequently they are grown as spheroids by the liquid overlay technique. Spheroids grown in this way were divided into ten groups of more than 50 cell aggregates. Three groups were coincubated with free TNF- in increasing dosages (100 ng/ml, 200 ng/ml and 1000 ng/ml); three groups were incubated with empty liposomes (0.2 mg/ml, 0.4 mg/ml and 2 mg/ml); three groups received liposomes which had been loaded with TNF-, and one group, which received no treatment, served as control.The diameter of the spheroids ranged from 80 m to 350 m. There was no significant difference in growth between the 3 groups treated with free TNF-. Comparing spheroids treated with TNF- with those which had been coincubated with empty liposomes, there was a significant difference (p<0.001) in growth, which correlated with the amount of liposomes. Similarly, free TNF- had a significantly (P<0.001) stronger growth-inhibiting effect as compared to liposomes loaded with TNF-. Comparing the groups treated with liposomes only to those treated with liposomes loaded with TNF-, the latter exhibited a more marked (although not significantly) growth-inhibiting effect.The preliminary conclusion is that the major growth-inhibiting effect seems to be mediated by the liposomes. This phenomenon is in agreement with results obtained in monolayer cultures.     

Nebulization of Liposomes. II. The Effects of Size and Modeling of Solute Release Profiles

A series of carboxyfluorescein (CF)-containing multilamellar vesicle (MLV) dispersions was prepared and extruded through polycarbonate membranes ranging in size from 0.2 to 5 µm. Vesicle dispersions were nebulized for 80 min using a Collison nebulizer, and the release of CF was monitored during nebulization. Solute retention was dependent upon the size of the vesicles and leakage ranged from 7.9 ± 0.4% (N = 3) for vesicles extruded through 0.2-µm filters to 76.8 ± 5.9% (N = 3) for liposomes that were not filtered. Solute release profiles obtained over 420-min nebulization periods conformed to a two-compartment kinetic model and exhibited a fast initial phase (k _l = 0.052 ± 0.0043) followed by a slow terminal phase (k ₂ = 0.0034 ± 0.00018). The results show that CF retention can be increased by nebulizing small vesicles and modeling suggests that the rate of CF leakage from the bilayers is faster than from the core of the liposomes.     

Liposomes and Nanoparticles in the Treatment of Intracellular Bacterial Infections

The treatment of infections caused by obligate or facultative intracellular microorganisms is difficult because most of the available antibiotics have either poor intracellular diffusion and retention or reduced activity at the acidic pH of the lysosomes. The need for antibiotics with greater intracellular efficacy led to the development of endocytosable drug carriers, such as liposomes and nanoparticles, which mimic the entry path of the bacteria by penetrating the cells into phagosomes or lysosomes. This Review assesses the potential of liposomes and nanoparticles in the targeted antibiotic therapy of intracellular bacterial infections and diseases and the pharmaceutical advantages and limitations of these submicron delivery systems.     

齐多夫啶半乳糖神经酰胺脂质体的制备及理化性质研究

目的 制备齐多夫啶半乳糖神经酰胺脂质体并对其理化性质进行研究。方法 采用两次乳化法，以半乳糖神经酰胺为主要膜材制备齐多夫啶半乳糖神经酰胺脂质体并进行形态学观察、检测其包封率和稳定性。结果 透射电子显微镜下观察齐多夫啶半乳糖神经酰胺脂质体为粒径均匀的球形或近球形的小单层颗粒；粒径范围为60～270nm，D50为140nm；包封率达72．5％，但10d后快速下降。结论 齐多夫啶半乳糖神经酰胺脂质体制备方法可行，需进一步提高包封率和稳定性。     

咪喹莫特脂质体与乳膏体外经皮扩散行为的比较

采用中和法制备咪喹莫特脂质体，研究了其体外经皮扩散行为并与咪喹莫特乳膏进行比较。制得的脂质体平均粒径为855nm，跨距为1．65，能经皮缓慢扩散，皮层的局部贮药量比之乳膏有增加，可减少药物全身吸收。     

小鼠口服多糖包覆胰岛素脂质体的降血糖作用小鼠口服多糖包覆胰岛素脂质体的降血糖作用

目的 研究壳聚糖和海藻酸钠两种多糖包覆胰岛素脂质体的小鼠po降血糖作用。方法 用逆相蒸发法制备胰岛素脂质体;用透射电镜和激光粒度仪测定它们的形态和粒径;用HPLC法和超速离心法测定包封率;用胃蛋白酶和胰蛋白酶溶液试验多糖包覆脂质体对胰岛素的保护作用;用酶-苯酚法测定小鼠po多糖包覆胰岛素脂质体后降血糖作用。结果小鼠po 0.1%壳聚糖和0.1%海藻酸钠包覆的胰岛素脂质体具有较好的降血糖作用。结论壳聚糖或海藻酸钠包覆的脂质体能减少胃蛋白酶或胰蛋白酶对胰岛素的降解并促进胰岛素po吸收。     

不同表面活性剂对两性霉素B脂质体体内外性质的影响

目的寻找与DSPE-PEG功能相似的表面活性剂修饰两性霉素B脂质体，以增加其在体内的稳定性，改善其体内分布，降低毒副作用。方法用薄膜超声法制备两性霉素B脂质体；比较用DSPE-PEG，Tween 80和Brij 35修饰后两性霉素B脂质体包封率、粒径分布、稳定性及组织分布的变化。结果两性霉素B脂质体的包封率最高为（91.2±1.6）％。修饰后的两性霉素B脂质体包封率提高，粒径减小，稳定性增加，肝、脾和肾中两性霉素B的浓度降低，脑中AmB的浓度提高。结论DSPE-PEG和Brij 35能提高脂质体逃避网状内皮系统吞噬的能力；Tween 80能增加两性霉素B在大鼠脑组织中的分布。     

脂质体粒径的分光光度法检测

目的确立分光光度法判断脂质体相对大小,为评估脂质体物理稳定性提供一种简便、快捷的方法。方法以Rayleigh-Gans-Debye理论为基础,固定脂质体膜材的种类、比例及其在溶液中的总量,分别用乙醇注入法和高压乳匀法制备不同粒径的空间稳定脂质体,以电镜法和热力学光散射法测得的粒径作为标准,找出不同方法制得脂质体在436 nm波长处的吸光度A与粒径D的关系。结果单位磷脂浓度的脂质体溶液在436 nm处log(A_436nm/C_p)与脂质体粒径的对数logD呈线性相关(r²≥0.93,n=5)。结论脂质体溶液的吸光度能反映脂质体相对大小,可作为一种评定脂质体物理稳定性的方法。