L-cysteine encapsulation in liposomes: effect of phospholipids nature on entrapment efficiency and stability

Liposomal entrapment of L-cysteine (L-CySH) could be a solution to enhance its oxidative stability and its intracellular bioavailability for glutathione (GSH) synthesis. This study addresses the influence of different factors (i.e. pH value (6.3 vs 7.4), antioxidant agents (EDTA or tocopherol (TO and nature of phosphatidylcholine (PC) (Soybean PC (SPC) vs hydrogenated SPC (HSPC)) to formulate and optimize Large Unilamellar Vesicles (LUVs) of L-CySH composed of PC/Cholesterol/ Phosphatidylglycerol (6:3:1). pH decrease (p = 0.0002) and substitution of SPC by HSPC (p < 0.001) reduced L-CySH oxidation. EE% (entrapment efficiency) varied from 0.98% +/- 0.54 (SPC, pH 7.4) to 6.46% +/- 1.37 (HSPC, pH 6.3) and was improved by decreasing pH (p = 0.011) and using HSPC (p < 0.0001). An immediate release of L-CySH was observed with SPC. On the contrary, with HSPC at pH 6.3, 42.0% +/- 1.2 and 73.0% +/- 1.7 remained encapsulated after 24h at 25 degrees C and 4 degrees C, respectively. In conclusion, HSPC offering both stronger rigidity and lesser propensity for peroxidation led to optimize L-CySH liposomal stability.     

Comparative study on preparative methods of DC-Chol/DOPE liposomes and formulation optimization by determining encapsulation efficiency

Three most commonly used preparative methods, dry-film, reverse phase evaporation and ethanol injection were employed to prepare cationic liposomes composed of DC-Chol and DOPE, respectively. The resulting samples were contrasted through morphology observation, particle size and zeta potential analysis. Sephadex filtration method with high selectivity was developed to determine the encapsulation efficiency of plasmid DNA-loaded cationic vectors, on this basis, cationic liposomes formulation was further optimized by applying Box Behnken design with encapsulation efficiency as evaluation index. The results showed that liposomes prepared by dry-film method were of best quality and stability, moreover, the optimum formulation of cationic liposomes and optimal value of each influencing factors were quantitatively obtained, measured value was highly consistent with predicted results. These findings preliminarily clarified the effect of preparative methods on performance of cationic liposome, as well as formulation factors on encapsulation efficiency, and will provide important methodological reference for further study of liposomes carriers for gene delivery.     

beta-Estradiol biodegradable microspheres: effect of formulation parameters on encapsulation efficiency and in vitro release

The purpose of this work was to study the effect of organic solvent and surfactant type on the in vitro release behavior in general and on the burst release in particular of beta-estradiol from PLA/PLGA microspheres. Also the effect of these variables on the encapsulation efficiency was investigated. The microspheres were prepared by solvent evaporation technique using dichloromethane (DCM), ethyl acetate (EtAc), tetrahydrofuran (THF), chloroform (CHCl3) or acetone (AC) as organic solvent and polyvinyl alcohol (PVA), Tween 80, sodium lauryl sulfate (SLS) or benzalkonium chloride (BKCI) as surfactant. The obtained microspheres were tested for encapsulation efficiency and in vitro drug release using 50% methanol/buffer pH 7.4 as dissolution medium. EtAC and PVA formulations showed the highest encapsulation efficiency and the lowest burst release. These microspheres were further characterized for particle size distribution, SEM and zeta potential. The results suggested that these materials could be starting materials to prepare a beta-estradiol biodegradable controlled delivery system.     

脂质体中蛋白类药物包封率的测定

目的建立脂质体中蛋白类药物包封率的测定方法。方法以牛血清白蛋白(bovine serum al-bumin,BSA)为模型蛋白,采用逆向蒸发法制备了平均粒径为5.129μm的BSA脂质体。采用离心-参照法测定BSA脂质体的包封率,并以凝胶过滤、超速离心、超滤和透析4种常用方法对包封率的结果进行比较。结果该方法平均回收率为101.7%,RSD为2.32%(n=5),BSA质量浓度在1.02～1 507.5 mg.L-1内线性关系良好。离心-参照法测定3批BSA脂质体的平均包封率为69.74%,RSD为1.34%。而其他几种方法测定同一批脂质体的包封率值偏高或偏低,即测定方法存在问题。结论该法简便灵敏,测得值真实、可靠,可以用于蛋白类药物脂质体中包封率的测定。     

Liposomes as a potential drug carrier for citicoline (CDP-choline) and the effect of formulation conditions on encapsulation efficiency.

In this paper we report the investigation of the potential of liposomes as drug carrier for citicoline (1; CDP-choline). The aim of our work is to improve the pharmacokinetic and pharmacodynamic parameters of the drug to facilitate the overcoming of the blood-brain barrier. The thermotropic behaviour of hydrated dispersions of various phospholipids and their mixtures containing 1 have been investigated by differential scanning calorimetry (DSC) to have a clear view of the interaction between the drug and the liposome phospholipids. By the values of transition peak temperature (Tm) and transition enthalpy (delta H) we note a strong interaction between 1 and the polar heads of L-alpha-dipalmitoylphosphatidic acid (DPPA) and L-alpha-dipalmitoylphosphatidylserine (DPPS), whereas there is not any considerable interaction between the drug and L-alpha-dipalmitoylphosphatidylcholine (DPPC) or L-alpha-dimyristoylphosphatidylcholine (DMPC); in any case no interaction occurs between 1 and the hydrophobic part of the phospholipid. So we conclude that all the drug is fitted into the aqueous spaces. The results of the encapsulation efficiency experiments demonstrate how the encapsulation capacity increase with using charged phospholipids, reaching the top with DPPA. Moreover, it was noted that the presence of Cholesterol (Chol) enhances the encapsulation capacity (EC) and drug content (DC) values of DPPC, a neutral phospholipid. The size of the liposomes was determined by light scattering (LS).     

Influence of physicochemical properties of fluoroquinolones on encapsulation efficiency in liposomes

Three fluoroquinolones, ciprofloxacin, norfloxacin and a newly synthesized compound (CNV-8912), were encapsulated in liposomes of DPPC at pH 7.40 and encapsulation efficiency was determined by two methods: spectrophotometry of isopropanol-lysed vesicles and HPLC. These methods are compared with a view to the reproducibility and sensitivity of each technique. Physicochemical properties such as octanol-buffer coefficients and pKs were determined in order to interpret the encapsulation efficiency values in terms of affinity for lipid environments and microspeciation at pH 7.40.     

黄芩苷脂质体的包封率测定和体外释放度考察

目的：测定黄芩苷脂质体的包封率，并考察其体外释放规律。方法：用逆相法制备黄芩苷脂质体。用葡聚糖凝胶G-50柱分离脂质体和游离药物，用HPLC法测定包封率。按照中国药典2005年版溶出度第三法考察黄芩苷脂质体体外释放规律。结果：测得黄芩苷脂质体平均包封率为54．4％，黄芩苷脂质体的体外释放规律符合一级动力学方程。结论：黄芩苷脂质体具有较高的包封率，在体外具有良好的缓释作用。     

L-cysteine encapsulation in liposomes: Effect of phospholipids nature on entrapment efficiency and stability

Liposomal entrapment of L-cysteine (L-CySH) could be a solution to enhance its oxidative stability and its intracellular bioavailability for glutathione (GSH) synthesis. This study addresses the influence of different factors (i.e. pH value (6.3 vs 7.4), antioxidant agents (EDTA or tocopherol (TO))) and nature of phosphatidylcholine (PC) (Soybean PC (SPC) vs hydrogenated SPC (HSPC)) to formulate and optimize Large Unilamellar Vesicles (LUVs) of L-CySH composed of PC/Cholesterol/Phosphatidylglycerol (6 : 3 : 1). pH decrease (p =?0.0002) and substitution of SPC by HSPC (p <?0.001) reduced L-CySH oxidation. EE% (entrapment efficiency) varied from 0.98% ±?0.54 (SPC, pH 7.4) to 6.46% ±?1.37 (HSPC, pH 6.3) and was improved by decreasing pH (p =?0.011) and using HSPC (p <?0.0001). An immediate release of L-CySH was observed with SPC. On the contrary, with HSPC at pH 6.3, 42.0% ±?1.2 and 73.0% ±?1.7 remained encapsulated after 24 h at 25°C and 4°C, respectively. In conclusion, HSPC offering both stronger rigidity and lesser propensity for peroxidation led to optimize L-CySH liposomal stability.     

新藤黄酸脂质体冻干粉的制备及其包封率测定

目的制备新藤黄酸脂质体冻干粉并测定其包封率。方法采用薄膜-超声法结合冷冻干燥法制备新藤黄酸脂质体冻干粉,以冷冻超速离心-高效液相色谱法测定包封率。结果电镜下观察所制备的脂质体形态规整,平均粒径为128.30 nm,包封率为83.74%。结论此法制备了包封率较高的新藤黄酸冻干脂质体。     

Determination of the encapsulation efficiency in liposomes obtained by the 'extruder method'

The encapsulation efficiency of carboxyfluorescein in liposomes obtained by the 'extruder method' has been determined. The encapsulating efficiency has also been related to the captured volume. The results show that the efficiency is proportional to the liposome diameter.     

不同制备方法对硫酸多黏菌素E脂质体包封率的影响

目的筛选硫酸多黏菌素E脂质体2种制备方法的最优处方,选择适合的制备方法。方法薄膜分散-超声法、逆相蒸发法制备脂质体,HPLC测定硫酸多黏菌素E脂质体包封率,正交设计法优化脂质体处方。结果制得的脂质体形状均匀、粒径适宜,包封率较高。结论逆相蒸发法较薄膜分散-超声法更适合于硫酸多黏菌素E脂质体的制备。     

Betamethasone-in-cyclodextrin-in-liposome: the effect of cyclodextrins on encapsulation efficiency and release kinetics

Lipophilic drugs have limited solubility in phospholipid systems, hence maximum entrapment levels in liposomes are known to be low. "Drugs-in-cyclodextrin-in-liposome" systems were previously proposed to overcome this drawback but studies were limited to betaCD and HPbetaCD. In some cases, other cyclodextrins may be more interesting than betaCD or HPbetaCD, such as methylated cyclodextrins. However, these cyclodextrins are known to extract lipid components from the lipid membrane, which may destabilize liposomes. We tested the influence of several cyclodextrins (betaCD, gammaCD, Dimeb, Trimeb, Crysmeb, Rameb, HPbetaCD and HPgammaCD) on the aqueous solubility of betamethasone by phase solubility diagrams and on the encapsulation efficiency in liposomes. The release kinetics of betamethasone was studied using Franz diffusion cells. We showed that release kinetics are directly correlated with encapsulation efficiency, which is closely related to betamethasone concentration in cyclodextrin complex solution. No liposome destruction was observed, even with the testing of methylated cyclodextrins at the highest concentration (40 mM). This can be explained by the fact that these cyclodextrins have a higher affinity for betamethasone than for cholesterol. This was proved by the comparison of phase solubility diagrams of both betamethasone and cholesterol.     

Comparing encapsulation efficiency and ultrasound-triggered release for protein between phospholipid-based microbubbles and liposomes

This work was to compare the encapsulation efficiency and ultrasound-triggered release for protein between microbubbles and liposomes. Bovine serum albumin (BSA) was used as a model. Final ratios between BSA and HPC in microbubbles and liposomes were 1 : 5, 1 : 7 and 1 : 10, respectively. Morphologic characteristics and contrast enhancement of loaded microbubbles and liposomes were measured. Encapsulation efficiency and ultrasound-stimulated release profile were detected. The mean size of loaded microbubbles and liposomes was 3.4 µm and 1.7 µm, respectively. Encapsulation efficiency of microbubbles had an inverse relationship with the ratio between BSA and HPC, while loaded liposomes remained nearly unchanged in the designed range of the ratio between BSA and HPC. Microbubbles resulted in significant enhancement of CnTi images. After ultrasound, more than 90% of the entrapped BSA was released from microbubbles, but less than 5% of BSA released from liposomes. Microbubbles are a promising delivery system for proteins.     

Effects of formulation parameters on encapsulation efficiency and release behavior of thienorphine loaded PLGA microspheres

To develop a long-acting injectable thienorphine biodegradable poly (d, l-lactide-co-glycolide) (PLGA) microsphere for the therapy of opioid addiction, the effects of formulation parameters on encapsulation efficiency and release behavior were studied. The thienorphine loaded PLGA microspheres were prepared by o/w solvent evaporation method and characterized by HPLC, SEM, laser particle size analysis, residual solvent content and sterility testing. The microspheres were sterilized by gamma irradiation (2.5 kGy). The results indicated that the morphology of the thienorphine PLGA microspheres presented a spherical shape with smooth surface, the particle size was distributed from 30.19?±?1.17 to 59.15?±?0.67μm and the drug encapsulation efficiency was influenced by drug/polymer ratio, homogeneous rotation speed, PVA concentration in the water phase and the polymer concentration in the oil phase. These changes were also reflected in drug release. The plasma drug concentration vs. time profiles were relatively smooth for about 25 days after injection of the thienorphine loaded PLGA microspheres to beagle dogs. In vitro and in vivo correlation was established.     

硫酸长春碱乳酸-羟基醋酸共聚物微球的处方和制备工艺研究

目的：制备硫酸长春碱生物可降解注射微球，考察处方和制备工艺对微球包封率及释放度的影响。方法：以乳酸-羟基醋酸共聚物（PLGA）为载体材料，分别采用O／O型和W／O／W乳化溶剂挥发法制备微球。结果：采用O／O型乳化溶剂挥发法制备的微球表面光滑无孔洞，内部结构致密；W／O／W型微球表面有较多皱褶，内部结构多孔。采用O／O型乳化溶剂挥发法制备的微球包封率在70％左右，明显高于W／O／W型乳化溶剂挥发法制备的微球，释药速度明显低于第2种方法制备的微球。采用O／O型乳化溶剂挥发法，以PLGA（50：50．10000）制备的微球在体外可持续释药21d以上。结论：硫酸长春碱PLGA微球的制备工艺可行，缓释特征明显，无突释效应。     

Effects of formulation factors on encapsulation efficiency and release behaviour in vitro of huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by UV/VIS spectrophotometry. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15 000 microspheres possessed a smooth and round appearance with average particle size of 50 microm or so. The encapsulation percentages of microspheres prepared from PLGA 15 000, 20 000 and 30 000 were 62.75, 27.52 and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30 000 microspheres to 3.97% of PLGA 15 000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increase in oil phase and PVA concentration decreased in aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30 degrees C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.     

Effects of formulation factors on encapsulation efficiency and release behaviour in vitro of huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using an o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by a UV/VIS spectrophotometer. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15,000 microspheres possessed a smooth and round appearance with average particle size of 50 microm or so. The encapsulation percentages of microspheres prepared from PLGA 15,000, 20,000 and 30,000 were 62.75%, 27.52% and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30,000 microspheres to 3.97% of PLGA 15,000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increased in the oil phase and PVA concentration decreased in the aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30 degrees C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.     

Effects of formulation factors on encapsulation efficiency and release behaviour in vitro of huperzine A-PLGA microspheres

To develop a long-acting injectable huperzine A-PLGA microsphere for the chronic therapy of Alzheimer's disease, the microsphere was prepared by using an o/w emulsion solvent extraction evaporation method based on a series of formulation design of the emulsion. The dialysis method was used for release analysis. The encapsulation efficiency and release amount of the microspheres were determined by a UV/VIS spectrophotometer. The morphology of the microspheres was observed by scanning electron microscopy. The distribution of the drug within microspheres was observed by a confocal laser scanning microscope. The results indicated that the PLGA 15?000 microspheres possessed a smooth and round appearance with average particle size of 50?µm or so. The encapsulation percentages of microspheres prepared from PLGA 15?000, 20?000 and 30?000 were 62.75%, 27.52% and 16.63%, respectively. The drug release percentage during the first day decreased from 22.52% of PLGA 30?000 microspheres to 3.97% of PLGA 15?000 microspheres, the complete release could be prolonged to 3 weeks. The initial burst release of microspheres with higher molecular weight PLGA could be explained by the inhomogeneous distribution of drug within microspheres. The encapsulation efficiency of the microspheres improved as the polymer concentration increased in the oil phase and PVA concentration decreased in the aqueous phase. The burst release could be controlled by reducing the polymer concentration. Evaporation temperature had a large effect on the drug release profiles. It had better be controlled under 30°C. Within a certain range of particle size, encapsulation efficiency decreased and drug release rate increased with the reducing of the particle size.     

The influence of frusemide formulation on diuretic effect and efficiency

AIMS: Changes in drug delivery rate may result in clinically important changes in drug effects. For the loop diuretic frusemide, it would be desirable to develop controlled release preparations, that could maintain an effective urinary excretion rate over a prolonged period of time. The aim of this study was to investigate the influence of frusemide formulation on frusemide recovery, diuretic effect and efficiency. METHODS: Twelve subjects were given 60 mg of four different frusemide controlled release formulations in a single-dose, double-blind, randomized 4-way cross-over design. The formulations were three study drugs with different extended dissolution rates (ER1Tab, ER2Tab and ER3Caps ) and one reference drug (LR). Urinary volume and contents of frusemide in urine were measured in samples collected over 24 h. RESULTS: Substantial differences in frusemide recovery and diuretic efficiency were observed between LR and all other formulations. At 24 h, mean total frusemide recoveries of ER1Tab, ER2Tab and ER3Caps were 52%, 36% and 57% lower, respectively, compared with LR (P<0.01). Also at 24 h, mean total diuretic efficiency for ER1Tab, ER2Tab and ER3Caps was 83%, 31% and 135% higher, respectively, compared to LR. The rapid dissolution and absorption of LR resulted in a high diuretic response from 0 to 3 h after dosing. However, from 0 to 24 h, there were no differences in diuretic response between the formulations. CONCLUSIONS: Controlled release formulations of frusemide with a low and extended rate of dissolution lead to a more prolonged absorption and subsequent diuresis, but still maintain a similar cumulative response, due to their higher diuretic efficiency.     

Filter extrusion of liposomes using different devices: comparison of liposome size, encapsulation efficiency, and process characteristics.

Liposomes were prepared by stepwise extrusion through 5, 1, 0.4, 0.2, 0.1 and 0.05 microm pore sizes using two different filter-extruders, the continuous high pressure device Dispex Maximator (CE) or alternatively the discontinuous Avestin LiposoFast (DE). The liposome dispersions obtained were compared in terms of particle size, lamellarity and encapsulation efficiency of calcein. The liposomes were smaller with CE than DE at all stages due to higher flow rates and pressure drops, except for final filter pore size (0.05 microm) where both preparations had similar sizes. The particle size analysis technique itself had a strong influence on the liposome sizes measured. For bigger liposomes (extruded through 0.4 microm filters) the Nicomp 370 revealed bigger volume-based mean particle sizes along with more stringent differences between volume-based and number-based diameters than the Malvern Zetasizer. In contrast, for small liposomes extruded through 0.05 microm filters, similar liposome sizes were found no matter which of the two PCS techniques or cryo-transmission electron microscopy was used. In congruence to the liposome sizes measured, encapsulation efficiencies were smaller for CE than DE at all filter stages except the final (0.05 microm). No lipid loss occurred and lyso-phosphatidylcholine formation was negligible irrespective of which extrusion technique was used.