白细胞介素2脂质体的制备及其抗肿瘤作用的研究

采用逆相蒸发法制备稳定的白细胞介素2（IL－2）大单层脂质体，对其包封率、稳定性及活性进行了测定。建立C57BL／6小鼠荷瘤动物模型，通过给荷瘤小鼠腹腔注射空白脂质体、单纯IL-2及IL-2脂质体来比较其在肿瘤生长中的抑制作用，结果3组抑癌率分别为4．26％、34．04％和54.60％。空白脂质体组与单纯对照组相比尤显著性差异（P＞0．05），脂质体-IL-2组与单纯IL-2组之间存在显著性差异（P＜0．05），抑瘤率提高了20.6％。     

Interleukin-2 liposomes for primary immune deficiency using the aerosol route.

This is the first report of aerosol interleukin 2 (IL-2) liposome administration to individuals with immune deficiency. Parenteral IL-2 therapy has shown beneficial effects in some patients with cancer, common variable immunodeficiency (CVID), and human immunodeficiency virus (HIV) but is problematic because of side effects including fever and malaise as well as local swelling (delayed type hypersensitivity like reaction) after each subcutaneous IL-2 injection. Provision of an IL-2:human albumin liposome formulation via the aerosol route had few side effects in a recent clinical trial in cancer patients. Details of good manufacturing practice (GMP) synthesis and analysis of IL-2 liposomes (N= 6 lots) made without albumin carrier protein and placebo liposomes (three lots) are presented. After centrifugation, IL-2 was closely associated with the liposome pellet (99%). Mean diameter of liposomes was 1.1 microm. Patient acceptance, safety, toxicity, and immune effects of IL-2 liposomes were studied in individuals with primary immune deficiency (N = 15) and subsequently, a larger cohort of patients with hepatitis C. Experience in the immune deficient patients is the subject of this report. Placebo liposomes (12 weeks) and IL-2 liposomes (12 weeks) were provided using a nebulizer. Aerosol placebo liposomes and IL-2 liposomes were well tolerated. No changes in chest X-ray or pulmonary function were seen. Since biologic activity of aerosol IL-2 liposomes has been seen in viral disease (hepatitis C), additional studies of aerosol IL-2 liposomes in individuals with hepatitis C and HIV are planned.     

白介素-2靶向5-氟尿苷棕榈酸酯脂质体的制备及细胞毒性研究

目的制备了白介素-2（IL-2）靶向5-氟尿苷棕榈酸酯（5-FURP）脂质体,并进行了体外细胞毒性,初步考察其对IL-2受体高表达的肿瘤细胞的靶向作用。方法采用逆相蒸发法制备5-FURP脂质体,通过交联剂将IL-2连接到脂质体的表面,得IL-2靶向5-FURP脂质体（IL-2-5FURP-L）;UV法测定包封率;用考马斯亮蓝结合法测定IL-2与脂质体的结合率;用MTT法测定脂质体对IL-2受体高表达的皮肤T细胞淋巴瘤Hut-102细胞的生长抑制作用。结果 IL-2-5-FURP-L的粒径为180 nm;药物平均包封率为91.3%;IL-2的结合率为56.0%;在pH7.4的释放介质中,脂质体具有缓释作用;MTT实验结果显示,IL-2-5-FURP-L呈剂量依赖性抑制肿瘤细胞的生长,72 h细胞毒性试验表明IL-2-5-FURP-L对Hut-102的杀伤作用（IC50=1.04μg.mL-1）明显优于5-FURP-L（IC50=6.11μg.mL-1）及5-FURP（IC50=7.35μg.mL-1）。结论 IL-2修饰的载药脂质体具有明显的抑瘤作用和主动靶向作用。     

Physicochemical characterization and skin permeation of liposome formulations containing clindamycin phosphate

This study was undertaken to evaluate the physicochemical properties and skin permeation of liposome formulations containing clindamycin phosphate (CP), especially when charge was imparted to the liposome. Five different liposome formulations were prepared using Phospholipon 85G (PL) and cholesterol (CH) by conventional lipid film hydration technique. Molar ratio of CH to PL was varied in the range of 0.16–1.0. Charged liposomes were prepared in the same way with addition of 1,2-dioleoyl-3-trimethylammonium-propane chloride salt (DOTAP) and 1,2-dimyristoyl-sn-glycero-3-phosphate monosodium salt (DMPA) as charge carrier lipid for cationic or anionic charge of the liposome, respectively. Fresh full-thickness mice skin was taken and used for skin permeation study using Keshary-Chien diffusion cell with 1.77 cm² diffusion area at 37°C. All liposome formulations prepared showed homogeneous size distribution with mean particle size of about 1 μm or less. Among the five liposome formulations prepared, formulation with the molar ratio of 0.5 showed the best result in the physicochemical properties such as polydispersity index, entrapment efficiency, size evolution, and ability of the liposome to retain CP as of entrapped in the vesicles. Charge-impartation of the formulation with cationic charge carrier lipid resulted in additional benefit in terms of inhibition of size evolution, the ability of the liposome to retain CP in the vesicles, and skin permeation. Steady state flux of the drug through the mice skin in the cationic liposome vesicles was 0.75 ± 0.01 μg/cm²h while that in the control (dissolved into mixed alcohol solution) was 0.17 μg/cm²h. One half molar ratio of CH to PL was optimal in terms of physicochemical properties of the liposome formulation containing CP, and incorporation of cationic charge carrier lipid appeared to provide additional benefits for the stability of the liposome formulation and skin permeation of the drug.     

阳离子脂质材料和聚乙二醇对脂质体细胞转染率及膜流动性的影响阳离子脂质材料和聚乙二醇对脂质体细胞转染率及膜流动性的影响

目的制备包封荧光素钠（FS）的脂质体，考察阳离子脂质材料（DC-chol）和聚乙二醇（PEG）对脂质体包封率、细胞转染率及膜流动性的影响。方法以FS作为模型物质，制备并分离脂质体，测定脂质体包封率；通过观察荧光光谱的变化考察FS与脂质体膜之间的相互作用；以HepG₂ 2.2.15为细胞模型观察脂质体对FS细胞转染率的影响；通过荧光偏振技术考察阳离子脂质材料和PEG对脂质体膜流动性的影响。结果阳离子脂质材料和PEG能提高脂质体包封率（0.64％～86.57％）、细胞转染率（2.18％～48.46％）及脂质体膜流动性，PEG分子质量的增大有利于包封率、转染率的提高，并增加脂质体膜的流动性。结论在脂质体处方中加入阳离子脂质材料和高分子量的PEG有利于提高包封率、细胞转染率及增加脂质体膜的流动性。     

Solubilization of Liposomes by Weak Electrolyte Drugs. I. Propranolol

The solubilization of dimyristoylphosphatidylcholine (DMPC) liposomes by a weak electrolyte drug, propranolol (PPL) hydrochloride, has been studied as a function of pH, [PPL], [DMPC], and temperature. The solubilization of liposomes at 40°C by 0.2 mM PPL occurred at different rates from 2.9 to 14.4 mM DMPC but converged at complete solubilization after 13 hr at pH 12.0. At the same [PPL], solubilization was complete after 18 days at pH 11.0, but incomplete solubilization occurred at pH 10.0 and not at all at lower pH's. In 14.4 mM DMPC liposomes, solubilization was gradual and proportional to the [PPL] from 0.001 to 0.10 mM up to 95 hr, then rapid thereafter. The [PPL] at which the solubilization efficiency began to increase rapidly was determined to be 0.078 mM. The rate of solubilization was also influenced by the fluidity of the bilayers, a sevenfold increase in the time for complete solubilization being observed upon cooling from 40 to 20°C. Surface tension (st) data confirmed a low critical micelle concentration (CMC) and continued decrease in the st above the CMC. It is concluded that the critical ratio of PPL to DMPC for solubilization occurs in localized regions of the bilayers, with total solubilization at different rates depending on the [PPL] and the physical properties of the liposomes. The processes may be used advantageously to prepare small vesicles or to extract lipids or proteins, more efficiently than detergents, from biological membranes.     

Differential Disposition of Soluble and Liposome-Formulated Human Recombinant Interleukin-7: Effects on Blood Lymphocyte Population in Guinea Pigs

The effects of liposome formulation on interleukin-7 (IL-T)-dependent lymphopoietic activity was investigated based on the pharmacokinetics and tissue distribution profile of soluble and liposome-formulated recombinant human IL-7. Using ¹²⁵I-IL-7, we determined the role of liposome formulation on in vivoIL-7 disposition by analyzing injection site, blood, tissue, and urinary kinetics. Following a 30- to 40-µg subcutaneous dose of soluble IL-7, most of the IL-7 was eliminated through urinary excretion within 24 hr. An equivalent subcutaneous dose of liposome-encapsulated IL-7 resulted in a peak level less than one-tenth that seen with soluble drug but produced sustained blood and urinary levels for 5 days. The bioavailability of liposome-encapsulated IL-7 was comparable to that of soluble IL-7, as determined by both blood and urinary data. Kinetic analysis of IL-7 at the subcutaneous injection site indicated that liposome encapsulation significantly reduced the rate of disappearance at the injection site. Studies with a mixture of 40% liposome-encapsulated and 60% soluble IL-7 gave an intermediate response between that of soluble IL-7 and that of liposome-encapsulated IL-7. Characterization of blood cells from IL-7-treated animals indicated that treatment with two weekly doses of mixed IL-7 liposomes (40% liposome encapsulated IL-7) significantly increased the total numbers of lymphocytes by day 14. In contrast, animals treated with soluble IL-7 on an identical dose and schedule did not produce any effect on blood lymphocytes. Collectively, liposome formulation provided a lower, but significantly sustained blood IL-7 level that enhanced IL-7 effects on blood lymphocyte numbers.     

Development and Characterization of a Liposome Preparation by a pH-Gradient Method

Abstract— A pH gradient across liposome bilayers was established in order to load a model drug (orciprenaline sulphate) into liposome vesicles. This method of liposome loading resulted in yields as high as 80–85% encapsulation. An eight-step process was designed to scale-up the process and was evaluated. In this process a diafiltration technique was successfully used to remove the excess orciprenaline sulphate present in the external medium. Finally, drug-loaded liposomes were lyophilized using lactose as an internal and external liposomal cryoprotectant. Five-month stability data for the liposomes is reported. An HPLC technique was used to determine the drug concentration and a laser light-scattering technique was employed to determine the liposome vesicle size and polydispersity factor. Liposomes prepared by the pH-gradient method showed high encapsulation efficiency. Upon storage at 2–8°C the vesicle size increased and encapsulation efficiency decreased with time. These phenomena are attributed to gradual fusion of liposomes and loss of drug to the extra-liposomal media.     

Encapsulation of ATP into liposomes by different methods: optimization of the procedure

Different methods and conditions for ATP incorporation into PEGylated liposomes were compared in order to obtain a preparation with a maximized ATP content. Such a preparation may find the application for the in vivo treatment of ischemic tissues suffering from an insufficient ATP supply. Several different methods of liposome preparation and purification were used and HPLC was employed to determine the concentration of ATP in the liposomes. Thin lipid film hydration produced vesicles with the lowest ATP encapsulation (ca. 5?mol%). A pH gradient method yielded liposomes with ca. 10?mol% of ATP. Reverse phase evaporation and freezing-thawing methods resulted in a maximum entrapment of ATP on the level of 36–38?mol%. The freezing-thawing method was chosen for further investigation because of its simplicity and absence of a need to use organic solvents. The separation of the non-entrapped ATP by gel-filtration, centrifugation or dialysis yielded virtually identical liposomal preparations. The incorporation of PEG (as PEG-distearoyl phosphatidylethanolamine, PEG-DSPE) into the liposomal membrane decreases the quantity of the entrapped ATP (from 38?mol% for liposomes with 0.5?mol% of PEG-DSPE to only 17?mol% for liposomes with 5?mol% of PEG-DSPE).     

Optimization of Lyophilization Conditions for Recombinant Human Interleukin-2 by Dried-State Conformational Analysis Using Fourier-Transform Infrared Spectroscopy

Purpose. Examination of the dried-state conformation of interleukin-2 (IL-2) was used to determine the pH conditions and stabilizers that provide optimal storage stability for the lyophilized product. Methods. Fourier-transform infrared spectroscopy and accelerated stability studies which examined solubility, aggregate formation, and covalent cross-linking were used. Results. Varying the pH in the absence of excipients resulted in dramatic differences in the dried state conformation of IL-2. At pH 7, IL-2 unfolds extensively upon lyophilization while at pH below 5 it remains essentially native. Additional unfolding was observed upon incubation at elevated temperatures. A strong direct correlation between the retention of the native (aqueous) structure during freeze-drying and enhanced stability is demonstrated. IL-2 prepared at pH 5 is approximately an order of magnitude more stable than at pH 7 with regard to formation of soluble and insoluble aggregates. A similar pH profile was observed in the presence of excipients, although the excipients alter the overall stability profile. Additional accelerated stability studies examined the stabilizers necessary for optimal stability. Conclusions. Excipients with the capacity to substitute for water upon dehydration better preserve the native structure resulting in enhanced stability. Those that have high glass transition temperatures provide the highest level of stability during storage, although they do not prevent dehydration induced unfolding.     

Chitosan‐coated antifungal formulations for nebulisation

Objectives The aim of this study was to produce and characterise amphotericin B (AmB) containing chitosan‐coated liposomes, and to determine their delivery from an air‐jet nebuliser. Methods Soya phosphatidylcholine : AmB (100 : 1) multilamellar vesicles were generated by dispersing ethanol‐based proliposomes with 0.9% sodium chloride or different concentrations of chitosan chloride. These liposomes were compared with vesicles produced by the film hydration method and micelles. AmB loading, particle size, zeta potential and antifungal activity were determined for formulations, which were delivered into a two‐stage impinger using a jet nebuliser. Key findings AmB incorporation was highest for liposomes produced from proliposomes and was greatest (approximately 80% loading) in chitosan‐coated formulations. Following nebulisation, approximately 60% of the AmB was deposited in the lower stage of the two‐stage impinger for liposomal formulations, for which the mean liposome size was reduced. Although AmB loading in deoxycholate micellar formulations was high (99%), a smaller dose of AmB was delivered to the lower stage of the two‐stage impinger compared to chitosan‐coated liposomes generated from proliposomes. Chitosan‐coated and uncoated liposomes loaded with AmB had antifungal activities against Candida albicans and C. tropicalis similar to AmB deoxycholate micelles, with a minimum inhibitory concentration of 0.5 µg/ml. Conclusions This study has demonstrated that chitosan‐coated liposomes, prepared by an ethanol‐based proliposome method, are a promising carrier system for the delivery of AmB using an air‐jet nebuliser, having a high drug‐loading that is likely to be effectively delivered to the peripheral airways for the treatment of pulmonary fungal infections.     

优福定脂质体的处方与工艺优化

目的:优化优福定脂质体的处方和制备工艺。方法:采用薄膜分散-冷冻干燥法制备优福定脂质体,以主药替加氟和尿嘧啶包封率为指标,应用正交试验优化其处方和制备工艺;考察其体外释放度并与普通片剂进行比较。结果:所得优化处方为磷脂与药物的重量比16∶1,磷脂与胆固醇的重量比7∶1,pH5.6的磷酸盐缓冲液为水合递质,水化温度为40℃。在此条件下,替加氟和尿嘧啶的平均包封率分别为(46.6±2.01)%、(48.7±1.49)%;脂质体的体外释放符合一级动力学方程,具有缓释作用。结论:优化得到的优福定脂质体处方工艺简便,稳定。     

5-Fluorouracil in topical liposome gels for anticancer treatment--formulation and evaluation

Liposome gels bearing an antineoplastic agent, 5-fluorouracil, intended for topical application have been prepared and drug release properties in vitro have been evaluated. Different formulations of liposomes were prepared by the film hydration method by varying the lipid phase composition (PL 90H/cholesterol mass ratio) and hydration conditions of dry lipid film (drug/aqueous phase mass ratio). Topical liposome gels were prepared by incorporation of lyophilized liposomes into a structured vehicle (1%, m/m, chitosan gel base). Also, hydrogels containing different concentrations of 5-fluorouracil were prepared and drug release properties were investigated. The rate of drug release from liposome gels was found to be dependent on the bilayer composition and the dry lipid film hydration conditions. Also, liposomes embedded into a structured vehicle of chitosan showed significantly slower release than hydrogels. The drug release obeyed the Higuchi diffusion model, while liposomes acted as reservoir systems for continuous delivery of the encapsulated drug.     

Development of a new topical system: Drug-in-cyclodextrin-in-deformable liposome

A new delivery system for cutaneous administration combining the advantages of cyclodextrin inclusion complexes and those of deformable liposomes was developed, leading to a new concept: drug-in-cyclodextrin-in-deformable liposomes. Deformable liposomes made of soybean phosphatidylcholine (PC) or dimyristoylphosphatidylcholine (DMPC) and sodium deoxycholate as edge activator were compared to classical non-deformable liposomes. Liposomes were prepared by the film evaporation method. Betamethasone, chosen as the model drug, was encapsulated in the aqueous cavity of liposomes by the use of cyclodextrins. Cyclodextrins allow an increase in the aqueous solubility of betamethasone and thus, the encapsulation efficiency in liposome vesicles. Liposome size, deformability and encapsulation efficiency were calculated. The best results were obtained with deformable liposomes made of PC in comparison with DMPC. The stability of PC vesicles was evaluated by measuring the leakage of encapsulated calcein on the one hand and the leakage of encapsulated betamethasone on the other hand. In vitro diffusion studies were carried out on Franz type diffusion cells through polycarbonate membranes. In comparison with non-deformable liposomes, these new vesicles showed improved encapsulation efficiency, good stability and higher in vitro diffusion percentages of encapsulated drug. They are therefore promising for future use in ex vivo and in vivo experiments.     

Effect of various formulation variables on the encapsulation and stability of dibucaine base in multilamellar vesicles

Formulation of local anesthetics in liposomal topical drug delivery system could provide a sustained and localized anesthesia. The aim of this study was to develop a liposomal dibucaine base (DB) local anesthetic delivery system. DB-loaded multilamellar vesicles (MLVs) were prepared through varying lipid composition, induced charge and pH of the hydration medium. Liposomes were characterized for morphology, size, entrapment efficiency (EE), in vitro drug release and stability including leakage stability. The percentage of drug entrapped in liposomes was found to be hydration medium pH dependent and charge dependent and more pronounced for negatively charged liposomes prepared using hydration medium of pH 9. In vitro release studies of liposomes have shown a sustained release of entrapped dibucaine compared to control solution. Results revealed that adjusting the various formulation variables of dibucaine base MLVs could yield stable and effective topical liposomal local anesthetic formulations.     

A novel and simple type of liposome carrier for recombinant interleukin-2

The strong interaction between recombinant interleukin-2 (IL-2) and liposome was characterized and its possible application to drug-delivery control considered. The liposomes were prepared with egg phosphatidylcholine, distearoyl-phosphatidylglycerol (DSPG), dipalmitoyl-phosphatidylcholine, dipalmitoyl-phosphatidylglycerol or distearoyl-phosphatidylcholine (DSPC). Small and hydrophobic liposomes were selected, which were composed of saturated and long-fatty-acid-chain phospholipids. When the composition and the mixture ratio of IL-2 and the liposomewere optimized, morethan 95% ofthe lyophilized IL-2 (Imunace, 350000 JRU) was adsorbed consistently onto the DSPC-DSPG liposome (molar ratio, 10:1; 25 micromol mL(-1); 30 nm in size). Merely mixing IL-2 lyophilized with liposome suspension is convenient pharmaceutically. After intravenous administration to mice, liposomal IL-2 was eliminated half as slowly from the systemic circulation as free IL-2, with more than 13 and 18 times more IL-2 being delivered to the liver and spleen, respectively. After subcutaneous administration of liposomal IL-2 to mice, the mean residence time of IL-2 in the systemic circulation was 8 times that of free IL-2. These results show that IL-2 consistently adsorbs onto the surface of liposomes after optimization of its composition and mixing ratio. Intravenous and subcutaneous administration to mice demonstrates the gradual release of IL-2. Further trials are warranted using these liposomes.     

Liposome formulation of poorly water soluble drugs: optimisation of drug loading and ESEM analysis of stability

Liposomes due to their biphasic characteristic and diversity in design, composition and construction, offer a dynamic and adaptable technology for enhancing drug solubility. Starting with equimolar egg-phosphatidylcholine (PC)/cholesterol liposomes, the influence of the liposomal composition and surface charge on the incorporation and retention of a model poorly water soluble drug, ibuprofen was investigated. Both the incorporation and the release of ibuprofen were influenced by the lipid composition of the multi-lamellar vesicles (MLV) with inclusion of the long alkyl chain lipid (dilignoceroyl phosphatidylcholine (C24PC)) resulting in enhanced ibuprofen incorporation efficiency and retention. The cholesterol content of the liposome bilayer was also shown to influence ibuprofen incorporation with maximum ibuprofen incorporation efficiency achieved when 4 micromol of cholesterol was present in the MLV formulation. Addition of anionic lipid dicetylphosphate (DCP) reduced ibuprofen drug loading presumably due to electrostatic repulsive forces between the carboxyl group of ibuprofen and the anionic head-group of DCP. In contrast, the addition of 2 micromol of the cationic lipid stearylamine (SA) to the liposome formulation (PC:Chol - 16 micromol:4 micromol) increased ibuprofen incorporation efficiency by approximately 8%. However further increases of the SA content to 4 micromol and above reduced incorporation by almost 50% compared to liposome formulations excluding the cationic lipid. Environmental scanning electron microscopy (ESEM) was used to dynamically follow the changes in liposome morphology during dehydration to provide an alternative assay of liposome stability. ESEM analysis clearly demonstrated that ibuprofen incorporation improved the stability of PC:Chol liposomes as evidenced by an increased resistance to coalescence during dehydration. These finding suggest a positive interaction between amphiphilic ibuprofen molecules and the bilayer structure of the liposome.     

Pharmacokinetics of oligodeoxynucleotides encapsulated in liposomes: effect of lipid composition and preparation method

1. The effect of the method employed to prepare liposomes and their lipid composition were evaluated in terms of the encapsulation efficiency and pharmacokinetic features of two oligodeoxynucleotides of a 21 mer: the normal (N-Odn) and the phosphorothioate (S-Odn) oligodeoxynucleotide. 2. Liposomes were prepared by the classical method of multilamellar vesicles (MV) and by the dehydration-rehydration method (DR). Two lipid mixtures were used to prepare liposomes--the predominant lipid being phosphatidylcholine (PC) and sphingomyelin (SM) respectively. 3. The DR method for liposome preparation provided the highest encapsulation efficiency, regardless of liposome lipid composition and the type of oligodeoxynucleotide involved (N-Odn or S-Odn). 4. The pharmacokinetics of free and liposome encapsulated oligodeoxynucleotides was studied in mouse following i.v. administration. Liposome encapsulated oligodeoxynucleotides exhibited a significantly lower plasma clearance and longer half-life and residence time than free oligodeoxynucleotides. The method used to obtain the liposomes affected plasma clearance, which was lower for liposomes elaborated by the DR method than for liposomes prepared with the MV method. The use of S-Odn in place of N-Odn decreased the plasma clearance of oligodeoxynucleotide when administered encapsulated in liposomes, regardless of the lipid composition and method used to obtain the liposomes.     

Formulation and Evaluation of a Folic Acid Receptor-Targeted Oral Vancomycin Liposomal Dosage Form

Purpose. To demonstrate utility of folic acid-coated liposomes for enhancing the delivery of a poorly absorbed glycopeptide, vancomycin, via the oral route. Methods. Liposomes prepared as dehydration-rehydration vesicles (DRVs) containing vancomycin were optimized for encapsulation efficiency and stability. A folic acid-poly(ethylene oxide)-cholesterol construct was synthesized for adsorption at DRV surfaces. Liposomes were characterized by differential scanning calorimetry (DSC) and assessed in vitroin the Caco-2 cell model and in vivoin male Sprague-Dawley rats. Non-compartmental pharmacokinetic analysis of vancomycin was conducted after intravenous and oral administration of solution or liposome-encapsulated vancomycin with or without 0.05 mole ratio FA-PEO-Chol adsorbed at liposome surfaces. Results. Optimal loading of vancomycin (32%) was achieved in DRVs of DSPC:Chol:DCP, 3:1:0.25 mole ratio (m.r.) after liposome extrusion. Liposomes released less than 40% of the entrapped drug after 2 hours incubation in simulated gastrointestinal (GI) fluid and simulated intestinal fluid containing a 10 mM bile salt cocktail. Incorporation of FA-PEO-Chol in liposomes increased drug leakage by 20% but resulted in a 5.7-fold increase in Caco-2 cell uptake of vancomycin. Liposomal delivery significantly increased the area under the curve of oral vancomycin resulting in a mean 3.9-fold and 12.5-fold increase in relative bioavailability for uncoated and FA-PEO-Chol-coated liposomes, respectively, compared with an oral solution. Conclusions. The design of FA-PEO-Chol-coated liposomes resulted in a dramatic increase in the oral delivery of a moderate-size glycopeptide in the rat compared with uncoated liposomes or oral solution. It is speculated that the cause of the observed effect was due to binding of liposome-surface folic acid to receptors in the GI tract with subsequent receptor-mediated endocytosis of entrapped vancomycin by enterocytes.     

Encapsulation of ATP into liposomes by different methods: optimization of the procedure

Different methods and conditions for ATP incorporation into PEGylated liposomes were compared in order to obtain a preparation with a maximized ATP content. Such a preparation may find the application for the in vivo treatment of ischemic tissues suffering from an insufficient ATP supply. Several different methods of liposome preparation and purification were used and HPLC was employed to determine the concentration of ATP in the liposomes. Thin lipid film hydration produced vesicles with the lowest ATP encapsulation (ca. 5 mol%). A pH gradient method yielded liposomes with ca. 10 mol% of ATP. Reverse phase evaporation and freezing-thawing methods resulted in a maximum entrapment of ATP on the level of 36-38 mol%. The freezing-thawing method was chosen for further investigation because of its simplicity and absence of a need to use organic solvents. The separation of the non-entrapped ATP by gel-filtration, centrifugation or dialysis yielded virtually identical liposomal preparations. The incorporation of PEG (as PEG-distearoyl phosphatidylethanolamine, PEG-DSPE) into the liposomal membrane decreases the quantity of the entrapped ATP (from 38 mol% for liposomes with 0.5 mol% of PEG-DSPE to only 17 mol% for liposomes with 5 mol% of PEG-DSPE).