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.     

脂质体包裹的反义寡核苷酸逆转耐甲氧西林金黄色葡萄球菌耐药性的研究

目的：用人工合成磷脂二棕榈酰磷脂酰胆碱（dipalmitoyl phosphatidylcholine，DPPC），二肉豆蔻酰磷脂酰甘油（dimyristoyl phosphatidylglycerol，DMPG）制备反义寡核苷酸阴离子脂质体并研究脂质体包裹的抑制耐甲氧西林金黄色葡萄球菌（methicillin resistant staphylococcus aureus，MRSA）耐药基因表达信号传导通路中BlaRlmRNA表达的反义寡核苷酸（antisense phosphothioate oligodeoxynucleotides，AS-ODNs）对MRSA耐药性的影响。方法：设计合成AS-ODNs；薄膜分散冻干法制备其脂质体；透射电镜观察脂质体的形态；离心纯化脂质体并用紫外分光光度计测定包封率、渗漏率；振荡法检测体外释放度；平板克隆形成实验计数菌落数CFU；微量法测定细菌生长曲线。结果：反义寡核苷酸阴离子脂质体大小均匀，为圆球体，包封率为77．38％，冷冻条件下保存1月后渗漏率为0．18％，体外释放度实验表明24h后约60％的药物从脂质体中释放，反义寡核苷酸脂质体可显著抑制MRSA生长，脂质体包裹的不同剂量的AS-ODNs中MRSA的菌落形成单位（CFU）与空白对照组比较明显减少，具有剂量依赖性，且效果明显优于未被脂质体包裹的AS-ODNs。结论：采用薄膜分散冻干法制备反义寡核苷酸阴离子脂质体，包封率较高，质量稳定，反义寡核苷酸脂质体能逆转MRSA的耐药性，效果明显优于单用AS-ODNs，可作为反义寡核苷酸进入细菌的载体。     

Preparation and in vitro activity of liposome encapsulated opioids

Four opiate molecules: morphine, naloxone, meperidine and codeine have been encapsulated in liposomes. The encapsulation efficiency has been studied as a function of the following parameters: liposome preparation method, lipid composition and opioid molecule hydrophobicity. The most important parameter as far as the entrapment efficiency is concerned is the liposome preparation method. The opioid activity of these molecules in vitro (Guinea Pig Ileum preparation) has been determined. No differences in the IC50 values could be found between encapsulated and free drug molecules.     

Preliminary data on the encapsulation of biologically active materials in liposomes

Multilamellar and unilamellar phospholipid liposomes were prepared and investigated as regards their properties and the capacity of encapsulating biologically active materials, such as CrO4-(2-)ions, basic dyes, proteins, DNA, as well as Sendai virus particles. The efficiency of encapsulation ranged from 10% for CrO4-(2-)ions to about 80% for toluidine blue; it was found to depend not only on the type of encapsulated material, but also on the method used for liposome preparation and on liposome composition.     

Dexamethasone Incorporating Liposomes: Effect of Lipid Composition on Drug Trapping Efficiency and Vesicle Stability

Effect of lipid composition on encapsulation and stability of dexamethasone (DXM) incorporating multilamellar vesicles (MLV) is studied. MLVs composed of phosphatidylcholine (PC) or distearoyl-glycero-PC (DSPC), with or without cholesterol (Chol), are prepared and the release of DXM during vesicle incubation in buffer or plasma proteins is evaluated. Incorporation of DXM is slightly higher in DSPC liposomes compared with PC, whereas the drug is displaced from liposomes, as the Chol content of liposome membranes increases. Plain lipid and Chol-containing liposomes lose similar fractions of vesicle-incorporated DXM during incubation in buffer or serum, whereas DXM release kinetics are similar (for each liposome type studied), implying that drug release is due mainly to dilution of liposome dispersions that leads to repartitioning of DXM.     

Dexamethasone incorporating liposomes: effect of lipid composition on drug trapping efficiency and vesicle stability

Effect of lipid composition on encapsulation and stability of dexamethasone (DXM) incorporating multilamellar vesicles (MLV) is studied. MLVs composed of phosphatidylcholine (PC) or distearoyl-glycero-PC (DSPC), with or without cholesterol (Chol), are prepared and the release of DXM during vesicle incubation in buffer or plasma proteins is evaluated. Incorporation of DXM is slightly higher in DSPC liposomes compared with PC, whereas the drug is displaced from liposomes, as the Chol content of liposome membranes increases. Plain lipid and Chol-containing liposomes lose similar fractions of vesicle-incorporated DXM during incubation in buffer or serum, whereas DXM release kinetics are similar (for each liposome type studied), implying that drug release is due mainly to dilution of liposome dispersions that leads to repartitioning of DXM.     

Effect of preparation method and cholesterol on drug encapsulation studies by phospholipid liposomes

Unilamellar liposomes, prepared from synthetic lipid mixture of DMPC and DMPG either by sonication or extrusion, were used to entrap water soluble and water insoluble molecules to investigate the efficacy of encapsulation by different liposome preparation methods. In the case of entrapment of hydrophilic protein cytochrome-C, the solutions were subjected to a series of ultrafiltration steps to eliminate any free protein outside the vesicles. It was observed that the protein could be encapsulated by the vesicles only if cholesterol was present in the bilayer. The release of cytochrome-C was observed spectrophotometrically upon vesicle-breakdown. The amount of protein encapsulated depended on the method of preparation and was found to be 10 times greater in extruded liposomes compared to those produced by sonication. Hydrophobic Vitamin E, on the other hand, could be encapsulated in the liposome bilayer, independently of the presence of cholesterol and the method of preparation. These fundamental results can be used to develop more efficient drug encapsulations and to have better understanding about their release.     

Long-circulating gadolinium-encapsulated liposomes for potential application in tumor neutron capture therapy

Gadolinium neutron capture therapy (Gd-NCT) is a promising cancer therapy modality. One of the key factors for a successful Gd-NCT is to deliver and maintain a sufficient amount of Gd in tumor tissues during neutron irradiation. We proposed to prepare a Gd delivery system by complexing a Gd-containing compound, diethylenetriaminepentaacetic acid (Gd-DTPA), with a polycationic peptide, poly-L-lysine (pLL), and then encapsulate the complexed Gd-DTPA into PEGylated liposomes. Complexation of Gd-DTPA with pLL not only enhanced the encapsulation efficiency of Gd-DTPA in liposomes, but also significantly limited the release of Gd-DTPA from the liposomes. A Gd-DTPA-encapsulated liposome formulation that contained 6.8+/-0.3 mg/mL of pure encapsulated Gd was prepared. The blood half-life of the Gd encapsulated into the liposome formulation was estimated to be about 24 h in healthy tumor-free mice. About 12 h after the Gd-encapsulated liposomes were intravenously injected into mice with pre-established model tumors, the Gd content in the tumors reached an average of 159 microg/g of wet tumor tissue. This Gd-DTPA encapsulated liposome may be used to deliver Gd into solid tumors for NCT and tumor imaging.     

Microencapsulated liposomes in controlled drug delivery: strategies to modulate drug release and eliminate the burst effect

The release of fluorescein isothiocyanate labeled bovine serum albumin (FITC-BSA) from alginate-microencapsulated liposomes was studied to evaluate the properties of this system for controlled drug delivery. Liposomes composed of phosphatidylcholine (PC) and cholesterol (Chol) (molar ratio 7:3) and of PC, phosphatidylglycerol (PG), and cholesterol (6:1:3) were encapsulated in alginate (Alg) crosslinked with Ca(2+) (Ca-Alg), Al(3+) (Al-Alg), and Ba(2+) (Ba-Alg). Capsules were coated with poly(l-ornithine) followed by a final alginate coat. A rapid initial burst of protein release was observed from liposomes encapsulated in Ca-Alg and Al-Alg. No burst was observed when liposomes were encapsulated in Ba-Alg, indicating that the crosslinking ions could significantly affect the release of entrapped protein. Also, the release from encapsulated liposomes varied significantly with liposome composition, especially with Ca-Alg as observed with encapsulation of PC, dioleoylphosphatidylcholine (DOPC), and DOPC/Chol liposomes. Cholesterol increased the leakiness of the liposomes after encapsulation. In all cases, the release from microencapsulated liposomes was much faster than that from free liposomes suggesting an interaction between the liposomes and the alginate. Differential scanning calorimetry supports the hypothesis that alginate was inserted into the lipid bilayer resulting in a rapid release of protein from microencapsulated liposomes. Moreover, it was observed that the degree of interaction between liposomes and alginate varied with liposome composition.     

甘草次酸阳离子脂质体的制备及稳定性考察

目的:制备甘草次酸阳离子脂质体,并研究其稳定性。方法:用乙醇注入法制备甘草次酸阳离子脂质体。考察其粒径、包封率、过氧化值、在血浆中的稳定性和放样稳定性等性质。结果:所得脂质体的粒径小而均匀,呈球形和类球形,包封率为(91.6±1.2)%;离心加速试验结果显示脂质体的稳定性参数KE值较小,脂质体在血浆中释放缓慢,在4℃下放置6个月,其外观、包封率、粒径等各项指标无明显改变。结论:制得的甘草次酸脂质体包封率较高,稳定性良好。     

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.     

Polyethylene glycol-coated liposomes for oral delivery of recombinant human epidermal growth factor

The present study was to investigate the feasibility of oral delivery of recombinant human epidermal growth factor (rhEGF). Polyethylene glycol (PEG)-coated liposomes containing rhEGF was prepared and evaluated for their stability and permeability in Caco-2 cells. In the animal study, we also determined plasma concentration and gastric ulcer healing effect after oral administration of rhEGF liposomes or the solution. Encapsulation of rhEGF into liposomes, suppressed the degradation in Caco-2 cell homogenate compared with the solution. The flux of rhEGF from dipalmitoylphosphatidylcholine (DPPC) liposome across Caco-2 cell monolayer from the apical to basolateral side was three times greater than that from phosphatidylcholine (PC) liposome or the solution. After oral administration of rhEGF liposomes or the solution in rats, the area under the concentration-time curve (AUC) of rhEGF increased 1.7- and 2.5-fold for PC and DPPC liposomes, respectively. The gastric ulcer healing effect was significantly increased in DPPC liposome compared with PC liposome and the solution. The enhanced curative ratio of rhEGF encapsulated into DPPC liposome may be due to the resistance to enzyme degradation, higher permeability and increased plasma AUC. Therefore, PEG-coated liposomes containing rhEGF could be used as an oral delivery formulation with enhanced encapsulation efficiency.     

Comparative Study of Separation of Non-encapsulated Drug from Unilamellar Liposomes by Various Methods

The purpose of this study was to compare the various methods available to separate non-encapsulated drug from large unilamellar liposomes (LUV). Multilamellar liposomes (MLV) were prepared by thin film hydration using distearoylphosphatidylcholine:cholesterol (2:1 molar ratio). MLVs were passed through a 0.2-μm polycarbonate membrane using an extruder to prepare LUVs. Particle size of liposome preparations was characterized using a submicron particle-size analyser. The non-encapsulated drug was separated by: filtering through Centrifree tubes; passing through gel (Sepharose-4B and Sephadex G-25M); passing through minicolumn; ficoll density gradient; protamine aggregation; or dialysis. The dialysis method was found to be unsuitable for separation of non-encapsulated drug due to equilibration of encapsulated drug as the free drug was dialyzed. The upper limit for lipid concentration was 5 mg mL^?1 using the Centrifree method. Separation using gel chromatography led to dilution of liposome preparation. Minicolumn and density gradient techniques did not lead to sample dilution, however the minicolumn method was tedious. The time required for separation of liposomes by protamine aggregation was longer for neutral liposomes. Thus it was concluded that the Centrifree was the fastest method to estimate encapsulation; the density gradient method was ideal to separate non-encapsulated drug; and protamine aggregation was the least expensive method to estimate encapsulation efficiency.     

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。     

槐定碱阳离子脂质体的制备及体外抗肿瘤活性的研究

目的制备槐定碱阳离子脂质体,并探讨其对肿瘤细胞的抑制作用。方法采用主动载药法制备槐定碱阳离子脂质体,并对其进行表征研究,采用MTS方法考察槐定碱阳离子脂质体对3种肿瘤细胞的抑制作用。结果制备得到的槐定碱阳离子脂质体呈类圆形,表面光滑,其平均粒径和聚分散指数分别为242.2 nm和0.180,表面电荷为+32.5 m V,其包封率和载药量分别为88.62%和5.97%。槐定碱阳离子脂质体对3种肿瘤细胞的IC50值均明显高于槐定碱,而空白阳离子脂质体对细胞并无明显的抑制作用。结论采用阳离子脂质体作为槐定碱的载体有利于将药物透过细胞膜,提高抗肿瘤作用,值得进行深入的系统研究。     

半枝莲总黄酮脂质体的制备及包封率的测定

目的：探讨半枝莲总黄酮脂质体的制备,建立半枝莲总黄酮含量测定方法,并测定其包封率。方法：采用薄膜分散法来制备半枝莲总黄酮脂质体,采用超速离心法分离脂质体及游离药物,采用紫外分光光度法（UV）测定半枝莲总黄酮含量,并计算其包封率。结果：薄膜分散法制备的半枝莲总黄酮脂质体颜色为深褐色,呈圆形或类圆形,平均粒径为0.54μm,分布均匀,脂质体的平均包封率为94.38%,符合2010版《中国药典》的要求。结论：薄膜分散法可以简单快速地制备半枝莲总黄酮脂质体,操作流程掌握容易,制备的脂质体形态较好、包封率较高;超速离心法与UV结合可以准确、可靠地测定半枝莲总黄酮脂质体的包封率。     

Immunoliposomes carrying plasmid DNA: preparation and characterization

The objective of this study was to characterize immunoliposomes carrying plasmid DNA with optimal encapsulation efficiency and antibody density. Plasmid DNA was encapsulated by the freezing/thawing method into liposomes composed of POPC (1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine), DDAB (didodecyl dimethyl ammonium bromide), DSPE-PEG 2000 (distearoyl phosphatidyl ethanolamine polyethylene glycol 2000) and DSPE-PEG 2000-maleimide. The liposomes carrying plasmid DNA were extruded through two stacked polycarbonate filters, of different pore size, to control the liposome size. Then, rat IgG molecules were conjugated to the liposomes. The immunoliposomes containing plasmid DNA were separated from the free plasmid DNA and unconjugated IgG by Sepharose CL-4B column chromatography. The DNA amount encapsulated was affected by DDAB (cationic lipid) concentration, the initial amount of plasmid DNA between 10 microg and 200 microg, the total lipid amount and plasmid DNA size, but not significantly by liposome size. By varying the ratio of DSPE-PEG 2000-maleimide to IgG, the number of IgG molecules per liposome was changed significantly.     

棓丙酯脂质体的制备与表征

目的制备棓丙酯脂质体,并对其进行理化性质的表征和释放度的评价。方法采用薄膜分散法制备棓丙酯脂质体,超滤离心法测定脂质体的包封率,正交设计优化处方,并对其包封率、粒径、Zeta电位、形态及体外释放行为进行综合评价。结果正交设计优化最终处方为磷脂浓度5 mg.mL-1、药脂比1∶5、磷脂胆固醇比5∶1、水化介质离子强度20 mmol.mL-1,所得脂质体包封率为89.6%、粒径为181.3 nm、Zeta电位为-21.8 mV、4 h体外释放达到80%。结论制备的棓丙酯脂质体包封率高,粒径小而均一,体外释放完全。     

HV12p-rPA血栓靶向脂质体的制备及体内溶栓实验

将通过蛋白质工程获得的抗凝溶栓双功能蛋白水蛭素12肽-瑞替普酶(HV12p-rPA)制备成靶向脂质体,并考察其体内溶栓效果。用薄膜分散-超声法制备HV12p-rPA脂质体,通过正交设计优化处方,采用碳二亚胺法偶联抗纤维蛋白原单克隆抗体(McAbSZ-65)制备HV12p-rPA靶向脂质体,采用大鼠颈总动脉血栓模型,考察HV12p-rPA靶向脂质体的体内溶栓效果。结果:最佳处方中HV12p-rPA脂质体的粒径为(142.45±1.20)nm,Zeta电位为(-30.63±0.48)mV,平均包封率为(91.59±1.39)%。靶向脂质体组(0.48±0.083)mg在相同剂量下(80k IU/kg)与PBS空白对照组(2.04±0.114)mg、游离HV12p-rPA组(1.2±0.100)mg和普通HV12p-rPA脂质体组(0.74±0.089)mg分别比较,其血栓干重明显减轻(P<0.05);靶向脂质体组与5倍剂量(400k IU/kg)的游离HV12p-rPA组(0.52±0.084)mg比较,其血栓干重较之偏轻(P>0.05)。制备出的靶向HV12p-rPA脂质体具有体内靶向溶栓效果。     

A novel approach to the pulmonary delivery of liposomes in dry powder form to eliminate the deleterious effects of milling

The effect of lyophilization and jet-milling on liposome integrity was investigated as a function of their ability to retain the encapsulated model drug on reconstitution of the dry products. The encapsulation efficiencies of the lyophilized and jet-milled formulations were determined at various concentrations of lactose. Lyophilization resulted in considerable leakage of the model drug at lower concentrations of lactose, and jet-milling further augmented the leakage for all the lyophilized formulations, with optimum retention obtained for formulations containing at least 10:1 molar ratio of lactose/lipid. In an attempt to overcome the deleterious effects of lyophilization and jet-milling, the feasibility of formulating phospholipid-based powders that result in spontaneous formation of liposomes in an aqueous environment has been investigated. Partitioning of three model drugs (viz., ciprofloxacin, CM3 peptide, and salbutamol sulfate) between the aqueous phase and spontaneously formed liposomes was determined in terms of encapsulation efficiency. The effects of several parameters, including lactose concentration, lipid composition, and lipid concentration on the encapsulation efficiency of these model drugs were investigated. The spontaneous formation of liposomes on dispersion of phospholipid-based powder formulations was further evidenced by freeze-fracture scanning electron microscopy. This novel approach for the delivery of liposomes in dry powder form appears promising because lyophilization is not involved and jet-milling of these powder formulations did not impact encapsulation efficiency. Jet-milled phospholipid-based powder formulations showed high encapsulation efficiencies of 96.2 +/- 1.4% for ciprofloxacin, 100% for CM3 peptide, and 45.3 +/- 3.1% for salbutamol sulfate compared with a high amount of leakage (> 50%) observed due to jet-milling of lyophilized liposome formulations encapsulating ciprofloxacin.