Reverse-phase Evaporation Liposomes Research Articles

Investigation of alternative organic solvents and methods for the preparation of long-circulating and pH-sensitive liposomes containing cisplatin

Recent studies using long-circulating and pH-sensitive liposomes containing cisplatin (SpHL-CDDP) have resulted in a formulation with improved pharmacokinetic, toxicity and tumor localization properties. In this study, SpHL-CDDP were prepared in both laboratory and pilot scales. This study evaluated the possibility of using the dehydration–rehydration method, as well as using alternative organic solvents (ethyl acetate/ethanol mixtures at 2:1 and 1:1 volume ratios), for the preparation of liposomes by the reverse-phase evaporation (REV) method. The influence of different concentrations of cisplatin (CDDP) (2.0, 1.0, 0.5 and 0.25 mg/mL) on the entrapment percentage and size of SpHL-CDDP was also investigated. In addition, carbohydrates were tested as cryoprotectants in a freeze–thaw study as a pretest to screen the type to be used in the freeze-drying process. A decrease in the encapsulation percentage of CDDP and an increase in the vesicle diameter could be observed for both liposome formulations prepared with ethyl acetate:ethanol mixtures, as compared with REV liposomes prepared with ethyl ether. It is important to note that after applying either quick or slow cooling, the mean diameter of SpHL (empty liposomes) proved to be similar when in the presence of cryoprotectants. In sum, the optimal processing conditions were achieved when using a 0.5 mg/mL CDDP solution, ethyl ether and the REV method, resulting in liposomal dispersions of mean diameters and homogeneities that were deemed suitable for intravenous administration.

Deformable liposomes by reverse-phase evaporation method for an enhanced skin delivery of (+)-catechin

Background: (+)-catechin, as the most common catechin isomer, is recognized to be an antioxidant which benefits the skin in many ways. The purpose of the present study was to prepare and evaluate a suitable liposomal delivery systems for (+)-catechin topical application.Methods: In this study, catechin-loaded conventional liposomal delivery system, deformable conventional liposomal delivery system and deformable liposomes prepared by reverse-phase evaporation (REV) method were compared. The three systems were characterized for liposome particle size, zeta-potential, entrapment efficiency, drug release, permeability across porcine skin and catechin deposition in the skin.Results: It was revealed that the size of deformable conventional liposomes before freeze-drying and deformable REV liposomes after freeze-drying range from 335.6 ± 71.7 nm to 551.1 ± 53.4 nm, respectively, which were considered to be suitable for skin delivery. The deformable REV liposomes had a higher aqueous volume and thus were able to entrap greater amounts of hydrophilic (+)-catechin (50.0 ± 5.9%) compared to conventional (30.0 ± 3.8%) and deformable conventional liposomes (36.1 ± 4.6%). All liposomal formulations exhibited a prolonged catechin release. Compared to deformable liposomes, the REV deformable liposomes showed a significantly better deposition of (+)-catechin while catechin solution did not permeate into the porcine ear skin.Conclusion: Among all formulations studied, deformable REV liposomes were considered to be favorable for catechin topical delivery.

The Incorporation and In-Vitro Release of Sodium Cromoglycate from Multilamellar and Reverse Phase Evaporation Liposomes

The Incorporation and In-Vitro Release of Sodium Cromoglycate from Multilamellar and Reverse Phase Evaporation Liposomes

Liposomes as an ocular delivery system for acetazolamide: in vitro and in vivo studies.

The purpose of this study was to formulate topically effective controlled release ophthalmic acetazolamide liposomal formulations. Reverse-phase evaporation and lipid film hydration methods were used for the preparation of reverse-phase evaporation (REVs) and multilamellar (MLVs) acetazolamide liposomes consisting of egg phosphatidylcholine (PC) and cholesterol (CH) in the molar ratios of (7:2), (7:4), (7:6), and (7:7) with or without stearylamine (SA) or dicetyl phosphate (DP) as positive and negative charge inducers, respectively. The prepared liposomes were evaluated for their entrapment efficiency and in vitro release. Multilamellar liposomes entrapped greater amounts of drug than REVs liposomes. Drug loading was increased by increasing CH content as well as by inclusion of SA. Drug release rate showed an order of negatively charged > neutral > positively charged liposomes, which is the reverse of the data of drug loading efficiency. Physical stability study indicated that approximately 89%, 77%, and 69% of acetazolamide was retained in positive, negative, and neutral MLVs liposomal formulations up to a period of 3 months at 4 degrees C. The intraocular pressure (IOP)-lowering activity of selected acetazolamide liposomal formulations was determined and compared with that of plain liposomes and acetazolamide solution. Multilamellar acetazolamide liposomes revealed more prolonged effect than REVs liposomes. The positively charged and neutral liposomes exhibited greater lowering in IOP and a more prolonged effect than the negatively charged ones. The positive multilamellar liposomes composed of PC:CH:SA (7:4:1) molar ratio showed the maximal response, which reached a value of -7.8 +/- 1.04 mmHg after 3 hours of topical administration.

Preparation and Quantitation of Small Unilamellar Liposomes and Large Unilamellar Reverse-Phase Evaporation Liposomes

Preparation and Quantitation of Small Unilamellar Liposomes and Large Unilamellar Reverse-Phase Evaporation Liposomes

Toxic effects of antileishmanial reverse-phase evaporation liposomes containing dicetyl phosphate in monkeys

AbstractLiposomes containing or lacking encapsulated pen-tavalent antimony (Sb), a widely used antileishmanial agent, were administered to cynomolgous monkeys to investigate possible toxicity. The liposomes consisted of either reverse-phase evaporation vesicles (REV) composed of dipalmitoyl phosphatidylcholine, choles- terol (CHOL), and dicetyl phosphate (DCP) or mul- tilamellar vesicles (MLV) composed of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol, with or without CHOL. Toxicity was observed in monkeys receiving REV containing or lacking Sb as evidenced by thrombocytopenia, splenomegaly, and hemorrhage. The severity of the symptoms was potentiated by two factors, the presence of Sb in REV and the frequency of REV administration. In contrast, no significant adverse reactions were observed in animals treated with MLV containing or lacking Sb. Since the main difference between REV and MLV was the presence of DCP in REV, this observation suggested that toxicity was due, at least part...

Encapsulation of ampicillin in reverse-phase evaporation liposomes: a direct evaluation by derivative spectrophotometry

Ampicillin has been entrapped in phospholipid vesicles by reverse-phase evaporation technique. The relationship between lipid composition and the encapsulation efficiency or the release of ampicillin-loaded liposomes was studied in vitro using a derivative spectrophotometry assay. The encapsulation degree was closely dependent on the lipid mixture used in liposome preparation: in particular, phosphatidylcholine (DPPC) vesicles containing cholesterol (CHO) or lipopolysaccharide (LPS) had a lower entrapment efficiency than liposomes prepared with DPPC alone, whereas the presence of cardiolipin (CD conferred an opposite trend. From the release kinetics it appeared that vesicles leaked the carried drug by a biphasic feature both dialyzing against buffer or in bulk solution. These observations indicate that for the in vivo use of ampicillin-loaded liposomes as chemotherapeutic agents one must pay attention to the lipid composition of the vesicle, in order to modulate the dose-response effect.

The effect of blood serum on the size and stability of phospholipid liposomes

Liposomes have been prepared by sonication (SUV) and reverse phase evaporation (REV) from dipalmitoylphosphatidylcholine (DPPC) and its mixtures with phosphatidylinositol (PI), stearylamine and cholesterol. The effect of rat and human blood serum on the liposomes has been investigated by measurement of the particle size in the serum-liposome mixtures by photon correlation spectroscopy in the range of serum protein concentration up to approx. 25 mg ml −1. At low serum protein concentrations the measured particle sizes exceed those calculated from the known sizes and concentrations of liposomes and serum particles in the mixtures: a result consistent with serum-induced aggregation of the liposomes, but the aggregates dissociate at higher serum protein concentration. The effect of serum on the release of encapsulated [ 14C]glucose from REV liposomes has been investigated over a range of serum protein concentration by gel filtration. At low serum concentration a proportion of the liposomes remain intact but as the serum concentration is increased the size of the liposomes decreases with concomitant release of encapsulated glucose. At high serum concentrations (approx. 24 mg protein per ml) the larger liposomes in the distribution are disrupted and some of the liposomal lipid becomes associated with serum protein. The results are discussed with reference to the effect of blood on the uptake of liposomes by rat liver.

Drug entrapment and release from multilamellar and reverse-phase evaporation liposomes

The entrapment of sodium cromoglycate was determined in multilamellar liposomes prepared from natural and synthetic phospholipids. Drug entrapment was low, but was increased by inclusion of cholesterol or stearylamine into vesicle bilayers. Reverse-phase evaporation vesicles entrapped greater amounts of drug than multilamellar liposomes of the same composition. The rate of drug efflux from liposomes was determined in vitro and was dependent upon bilayer composition and the method of preparation.

Transfer of liposome-encapsulated plasmid DNA to Bacillus subtilis protoplasts and calcium-treated Escherichia coli cells.

Protoplasts of Bacillus subtilis 168 trpC2 str and cells of Escherichia coli SK 1590 after treatment with calcium chloride were transformed to tetracycline resistance with the recombinant plasmid pUN82 entrapped in the reverse phase evaporation liposomes. Frequency of transfer was 4 X 10(-4)% in B. subtilis and 8 X 10(-6)% in E. coli.

Infection of evacuolated turnip protoplasts with liposome-packaged cauliflower mosaic virus

The infectivity of reverse phase evaporation (REV) liposome-encapsidated cauliflower mosaic virus (CaMV) to turnip protoplasts was tested. The uptake of neutral or negative liposomes was stimulated by polyethylene glycol (PEG), while high levels of uptake of positive liposomes were obtained both in the absence and presence of PEG. The delivery of the vesicle contents to the protoplasts paralleled the uptake of liposomes. CaMV delivered to turnip protoplasts was degraded during the early period of culture. No increase in the amount of CaMV DNA could be detected on longer periods of culture. In contrast, when protoplasts were evacuolated prior to addition of REV liposomes, an increase in the amount of CaMV DNA was noted after some initial degradation of the input DNA.

Size and permeability of liposomes extruded through polycarbonate membranes

The effects of extrusion of multilamellar liposomes (MLV) and reverse-phase evaporation liposomes (REV) on their sizes and permeabilities were studied. Extrusion through polycarbonate membranes decreases the mean size of both liposomes with improved homogeneity of the size distribution. Extrusion increases moderately the water permeability (k¯ W)of lecithin-only MLV and REV. But, the increase in k¯ W is small for the cholesterol-containing REV. The increase in k¯ W is not due to the decrease in size or the lamellar number, but to the increased disorder of the bilayer. The permeabilities of amino acids (k¯ A) are increased by extrusion as well as by sonication. The increase in k¯ A is considered to be due to the decrease in the lamellar number. The addition of digitonin into lecithin-cholesterol MLV eliminates the condensing effect of cholesterol, i.e. the k¯ W of lecithin-cholesterol MLV increased to the level of lecithin-only MLV. This suggests that digitonin-cholesterol complex forms separated domains in the PC bilayer.

Liposome uptake into human colon adenocarcinoma cells in monolayer, spinner, and trypsinized cultures.

The purpose of this study was to begin investigating the nature of liposome interactions with colon tumor cells. Thus, experiments were performed to study the uptake and incorporation of multilamellar and of reverse-phase evaporation liposomes of neutral charge into monolayers, suspended spinner cultures, and trypsinized cells of a human colon adenocarcinoma cell line, LS174T. The results showed that the same tumor cells cultured under each condition exhibited a distinct pattern of vesicle uptake as determined at 0, 15, 30, 60, and 120 min. In monolayer cultures of LS174T cells, the uptake of liposomes bearing [3H]actinomycin D in the lipid bilayers was linear throughout the incubation period. In contrast, in trypsinized and spinner suspension cultures, uptake of liposomes was biphasic. There was a proportional uptake of both liposome (labeled with [3H]phosphatidylcholine or [14C]cholesterol) and of actinomycin D (trace labeled with 3H) into the cells under all culture conditions, indicating quantitative delivery of the drug with the intact lipid vesicle. Although the amount of actinomycin D presented to tumor cells by the two liposomes was equivalent, reverse-phase evaporation liposomes were more effective than multilamellar vesicles in inhibiting uridine uptake. In the presence of excess liposomes (10 times the uptake studies), saturation of the tumor cell surface occurred by 120 min. However, the liposomes remained accessible to enzymatic removal for 60 min. Liposome-saturated tumor cells remained refractory to further binding of liposomes for at least 2 hr. The results thus revealed that differences in cell uptake were due to the state of the target cells and not the liposome types, or their differential leakage of labels.