Development and in vitro evaluation of a liposome based implant formulation for the decapeptide cetrorelix.

Semisolid phospholipid dispersions of vesicular morphology, so-called vesicular phospholipid gels (VPGs), were prepared by high-pressure homogenisation and tested in vitro for their suitability as implantable sustained release system for the decapeptide cetrorelix, a potent LH-RH antagonist. The VPGs contained 300-500 mg/g egg phosphatidylcholine (E80) and 0.5-10 mg/g cetrorelix acetate (CXA). The in vitro release experiments showed a wide variability of the system in release, ranging from complete release within less than 24 h (0.5mg/g CXA; 400 mg/g E80) to a predicted 80% sustained release over 3 months (8.6 mg/g CXA; 280 mg/g E80). Erosion of the phospholipid matrix, i.e. release of phospholipid vesicles was found to be the main release mechanism, following zero order or first order kinetics depending on the composition of the VPG. CXA-concentration dependent drug-drug or drug-lipid interactions are assumed to be responsible for the change in release kinetics and the decrease of CXA release at high concentrations of the peptide. Multivariate analysis revealed that both lipid concentration and peptide concentration and also the interactions between the two factors are significant factors for the release rate of the peptide. In summary: based on the presented in vitro release data sustained release of therapeutically relevant CXA doses over up to 6 weeks appears feasible. VPGs are thus considered as a promising new approach for the sustained release of peptide hormones.     

Sterilization stability of vesicular phospholipid gels loaded with cytarabine for brain implant

The aim of this study was to investigate the sterilization stability of cytarabine (Ara-C) loaded vesicular phospholipid gels (VPGs). VPGs were prepared by high pressure homogenization method intended for the treatment of glioblastoma multiforme (GBM) in brain as injectable implant. The particle size of VPGs after redispersion was 119.6 ± 66.24 nm, and entrapment efficiency (EE) was 32.6 ± 2.1%. Drug release in vitro from VPGs sustained for 80 h with 48.1% initial release within 1h, and rheological studies demonstrated a gel-like behavior. Comparatively, after autoclaved sterilization, increased particle size and EE were obtained as 165.6 ± 71.89 nm and 62.6 ± 2.3%, respectively. Additionally, characteristics of drug release were significantly altered with obviously prolonged release time to 450 h and remarkable reduced initial release to 24.7%. Also, the viscoelasticity was reinforced with clearly decreased fluidity. This result could be explained by the fusion of small vesicles witnessed in TEM observation, which resulted in percentages change of vesicle groups with different size. However, reduced Ara-C and increased lysophosphatidylcholine (LPC) were observed. Among the stabilizers, addition of sodium sulfite showed best effects with high stability of Ara-C and phospholipids. This may be explained by the presence of SO(3)(-), free radicals produced by sodium sulfite. Being an hydroxyl radical scavenger, it can reduce the generation of HO free radicals. These results show that, with addition of appropriate stabilizers, VPGs can be autoclaved with high stability, and it is a promising dosage form for treatment of GBM after injection into resectable or nonresectable neoplasms with sustained release properties.     

Preparation and characterization of semi-solid phospholipid dispersions and dilutions thereof

Highly concentrated, viscous to semi-solid phospholipid dispersions with phosphatidylcholine (PC) contents up to 600 mg/g or 780 mM were obtained by high-pressure homogenization. Dilution of these pastes with excess buffer led to ‘classical' liposome dispersions. The dilution technique determined the homogeneity of the liposome dispersions. Handshaking yielded heterogeneous dispersions, which according to cryo-electron microscopy contained large multivesicular vesicles (MVVs) as well as small unilamellar vesicles (SUVs). By using a ball mill for dilution, however, the phospholipid pastes could be completely transferred into uniform SUVs with mean diameters of about 20–40 nm. The absence of bigger particles could be demonstrated both by a membrane filtration test through 0.2 μm pore filters and photon correlation spectroscopy. Lipid paste formation and subsequent dilution into liposomes led to high encapsulation efficiencies of the hydrophilic model compound 5,6-carboxyfluorescein. For true SUV dispersions, encapsulation efficiencies rose with increasing lipid contents up to a maximum of over 45% at original lipid contents of 600 mg/g. According to geometrical considerations, the packing of SUVs reaches densest sphere packing at this lipid content. In conclusion, semi-solid, vesicular PC pastes can be diluted by ball milling into homogeneous SUV dispersions with high encapsulation efficiency for hydrophilic compounds.     

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.     

Development and characterization of oleic acid vesicles for the topical delivery of fluconazole

Fatty acids have been widely used as adjuvant, vehicles in drug delivery viz penetration enhancers in topical delivery and in polymeric micelles to provide sustained release. However, the present investigation aims at exploring the potential of fatty acid vesicles for the topical delivery of fluconazole. Vesicles were prepared by film hydration method using oleic acid as a fatty acid principal component. Developed vesicles were characterized for size, size distribution, shape, in vitro release, pH dependent and storage stability, skin irritation study, and ex-vivo skin permeation. Penetration behavior of vesicles was further evaluated and elucidated using confocal microscopic study. Optical microscopy and TEM studies confirmed vesicular dispersion of fatty acid. The vesicles possessed higher entrapment efficiency (44.11%) with optimum vesicle size and homogeneity in regard to size distribution (PDI?=?0.234?±?0.016) at 7:3 oleic acid-to-fluconazole ratio. In vitro drug release study suggested sustained release of drug from the vesicles. The release pattern followed Higuchian kinetics. The vesicles were fairly stable at refrigerated conditions. Ex-vivo skin permeation and confocal microscopic studies suggested that oleic acid vesicles penetrate the stratum corneum and retain the drug accumulated in the epidermal part of the skin. On the basis of sustained release behavior and skin retention it can be inferred that oleic acid vesicles can serve as a potential carrier for the topical localized delivery of bioactives.     

Construction of nanoscale multicompartment liposomes for combinatory drug delivery

Liposomes are clinically used delivery systems for chemotherapeutic agents, biological macromolecules and diagnostics. Due to their flexibility in size and composition, different types of liposomes have been developed varying in surface and structural characteristics. Multicompartment liposomes constitute an attractive drug carrier system offering advantages in terms of inner vesicle protection, sustained drug release and possibility for combinatory (cocktail) therapies using a single delivery system. However, all previously described methodologies for multicompartment or multivesicular liposomes resulted in micrometer-sized vesicles limiting most pharmaceutical applications. In this work we report formulation of nanoscale multicompartment liposomes which maybe applicable for systemic administration. A small unilamellar vesicle (SUV) aqueous dispersion (DOPC:DOPG:CHOL) was used to hydrate a dried film of different lipid contents (DMPC:CHOL), followed by extrusion. The system was characterised by techniques such as photon correlation spectroscopy (PCS), zeta potential measurement, transmission electron microscopy (TEM) and laser scanning confocal microscopy (LSCM). We observed a single, multicompartment vesicle population composed of the two different bilayer types of approximately 200 nm in mean diameter rather than a mixture of two independent vesicle populations. In the case of tumour therapy, such multicompartment liposome systems can offer a single carrier for the delivery of two different modalities.     

Nebulization of ultradeformable liposomes: The influence of aerosolization mechanism and formulation excipients

Ultradeformable liposomes are stress-responsive phospholipid vesicles that have been investigated extensively in transdermal delivery. In this study, the suitability of ultradeformable liposomes for pulmonary delivery was investigated. Aerosols of ultradeformable liposomes were generated using air-jet, ultrasonic or vibrating-mesh nebulizers and their stability during aerosol generation was evaluated using salbutamol sulphate as a model hydrophilic drug. Although delivery of ultradeformable liposome aerosols in high fine particle fraction was achievable, the vesicles were very unstable to nebulization so that up to 98% drug losses were demonstrated. Conventional liposomes were relatively less unstable to nebulization. Moreover, ultradeformable liposomes tended to aggregate during nebulization whilst conventional vesicles demonstrated a "size fractionation" behaviour, with smaller liposomes delivered to the lower stage of the impinger and larger vesicles to the upper stage. A release study conducted for 2h showed that ultradeformable liposomes retained only 30% of the originally entrapped drug, which was increased to 53% by inclusion of cholesterol within the formulations. By contrast, conventional liposomes retained 60-70% of the originally entrapped drug. The differences between ultradeformable liposomes and liposomes were attributed to the presence of ethanol or Tween 80 within the elastic vesicle formulations. Overall, this study demonstrated, contrary to our expectation, that materials included with the aim of making the liposomes more elastic and ultradeformable to enhance delivery from nebulizers were in fact responsible for vesicle instability during nebulization and high leakage rates of the drug.     

Liposomes encapsulating polymeric chitosan based vesicles--a vesicle in vesicle system for drug delivery

Drug delivery systems comprising vesicles prepared from one amphiphile encapsulating vesicles prepared from a second amphiphile have not been prepared previously due to a tendency of the bilayer components of the different vesicles to mix during preparation. Recently we have developed polymeric vesicles using the new polymer-palmitoyl glycol chitosan and cholesterol in a 2:1 weight ratio. These polymeric vesicles have now been encapsulated within egg phosphatidylcholine (egg PC), cholesterol (2:1 weight ratio) liposomes yielding a vesicle in vesicle system. The vesicle in vesicle system was visualised by freeze fracture electron microscopy. The mixing of the different bilayer components was studied by monitoring the excimer fluorescence of pyrene-labelled polymeric vesicles after their encapsulation within egg PC liposomes or hexadecyl diglycerol ether niosomes. A minimum degree of lipid mixing was observed with the polymeric vesicle-egg PC liposome system when compared to the polymeric vesicle-hexadecyl diglycerol ether niosome system. The polymeric vesicle-egg PC vesicle in vesicle system was shown to retard the release of encapsulated solutes. 28% of 5(6)-carboxyfluorescein (CF) encapsulated in the polymeric vesicle compartment of the vesicle in vesicle system was released after 4 h compared to the release of 62% of encapsulated CF from plain polymeric vesicles within the same time period.     

Liposome preparation using a hollow fiber membrane contactor--application to spironolactone encapsulation

In this study, we present a novel liposome preparation technique suitable for the entrapment of pharmaceutical and cosmetic agents. This new method uses a membrane contactor in a hollow fiber configuration. In order to investigate the process, key parameters influence on the liposome characteristics was studied. It has been established that the vesicle size distribution decreased with the organic phase pressure decrease, the phospholipid concentration decreases and the aqueous to organic phase volume ratio increases. Liposomes were filled with a hydrophobic drug model, spironolactone that could be used for a paediatric medication. The mean size of drug-free and drug-loaded liposomes was, respectively, 113 ± 4 nm and 123 ± 3 nm. The zeta potential of drug-free and drug-loaded liposomes was, respectively, -43 ± 0.7 mV and -23 ± 0.6 mV. High entrapment efficiency values were successfully achieved (93 ± 1.12%). Transmission electron microscopy images revealed nanometric sized and spherical shaped oligo-lamellar vesicles. The release profile showed a rapid and complete release within about 5h. Additionally, special attention was paid on process reproducibility and long term lipid vesicles stability. Results confirmed the robustness of the hollow fiber module based technique. Moreover, the technique is simple, fast and has a potential for continuous production of nanosized liposome suspensions at large scale.     

Niosomes as carriers for tretinoin. I. Preparation and properties

Tretinoin-loaded niosomes were prepared from polyoxyethylene (4) lauryl ether, sorbitan esters and a commercial mixture of octyl/decyl polyglucosides, in the presence of cholesterol and dicetyl phosphate. Liposomes made of hydrogenated and non-hydrogenated phosphatidylcholine were also prepared as a comparison reference. A study was made of the influence of vesicle composition and preparation method on the vesicle structure (MLV, LUV, SUV), size distribution, entrapment efficiency and in vitro release of incorporated tretinoin. Results showed that in the presence of cholesterol all the amphiphiles used were able to form stable vesicle dispersions with or without tretinoin. Vesicle sizes were dependent on the preparation method, bilayer composition and drug load. Multilamellar (MLV) vesicles were larger than extruded (LUV) and sonicated (SUV) vesicles while drug-loaded vesicles were generally smaller than empty ones. Entrapment efficiencies of tretinoin were always very high especially for multilamellar (91-99%) and extruded (88-98%) vesicles. The in vitro release of tretinoin from the prepared vesicular formulations was studied using the vertical Franz diffusion cells. The rate of drug release through a Silastic membrane from a liposomal and niosomal tretinoin dispersion was generally faster than from a tretinoin solution. Release data showed that tretinoin delivery is mainly affected by the vesicular structure and that tretinoin delivery increased from MLVs to LUVs to SUVs.     

Formulation Development and in vitro Characterization of Proliposomes for Topical Delivery of Aceclofenac

Non-steroidal antiinflammatory drugs are routinely prescribed for the patients with rheumatic disease and such patients are at increased risk of serious gastrointestinal complications, when non-steroidal antiinflammatory drugs administered by oral route. The aim of the present study was to develop and characterized a vesicular drug carrier system (proliposome) for topical delivery of aceclofenac to overcome the problems related with oral route. Aceclofenac proliposome were prepared by the film-deposition on carriers method and characterized for size and surface morphology, drug content in both proliposomes and liposomal system, percent yield, in vitro drug release studies and drug permeation studies. The prepared system was also characterized for drug-excipients interaction by Fourier transform infrared spectrophotometer and stability studies. The size and surface morphology were studied using optical microscopy, scanning electron microscopy and transmission electron microscopy. A spherical shape of reconstituted aceclofenac liposome with an average vesicular size of about 500 nm was observed in photomicrographs. The maximum entrapment efficiency of reconstituted liposomes was 80.31% whereas the drug content in proliposomes was found to be more than 90%. In vitro release of drug was significantly retarded indicating sustained release of aceclofenac from proliposomes. Stability study was performed at various temperatures indicating that aceclofenac proliposomes are stable at lower temperature.     

Phospholipid-detergent systems: effects of polysorbates on the release of liposomal caffeine

It is well known that surfactants are capable of interacting with phospholipid vesicles leading to different aggregated structures and finally to mixed micellar systems. By means of diffusion experiments with Valia-Chien cells the effect of different vesicular structures (MLV and SUV) and that of three polysorbates on the release of a model drug (caffeine) from various vesicle formulations was studied. Obtained results indicate that a remarkable delayed/sustained caffeine release is obtained only with the MLV preparations and that the presence of increasing surfactant concentrations initially leads to a further decrease of drug delivery rate and then to a faster release that reaches a maximum when only mixed micelles are present. The variation of the observed effects with the different tested surfactants, in relation to their lipophilicity (HLB values), is also discussed.     

1-O-Alkylglycerol vesicles (Algosomes): their formation and characterization

1-O-alkylglycerols (ALKG) have exhibited several biological activities and a prominent effect on blood-brain barrier permeability. They have markedly improved brain uptake of cancerostatic agents. Since ALKG are amphiphilic, we explored their tendency to assemble into bilayer vesicles, which can be applied as carriers for drugs. Vesicles (Algosomes) were formed by film hydration method using ALKG (tetra-, penta-, hexa-, hepta-, octa- or nona-decylglycerols) in combination with cholesterol (CHOL) and dicetyl phosphate (DCP) (1-O-alkylglycerol:CHOL:DCP in 45:45:10 molar ratio). On microscopic examination, the algosomes were found to be conspicuously spherical and the dispersion was a mixture of multi-lamellar and small-unilamellar vesicles. Phase transition temperatures of 1-O-hexadecylglycerol (HXDG) and CHOL mixtures were tested by differential scanning calorimetry (DSC). The changes in phase transition temperatures indicate the vesicle forming tendency of ALKG in presence of CHOL. Alkyl chain length dependent variations in vesicle size, zeta-potential (ZP) and capture volume (CV) could not be observed. Vesicles of 1-O-tetradecylglycerol (TTDG) showed improvement in CV with increase in CHOL content from 15 to 55 mol%. However the vesicle size decreased. On challenging algosomes with hypertonic salt solution [potassium iodide (KI) in water], vesicle size decreased and thus algosomes were found to be osmotically sensitive. Algosome dispersions on addition of higher concentrations of KI (40-100 mM) brought about increases in vesicle size and at concentrations 60 mM and above showed aggregation. All vesicular dispersions were stable for only a few days.     

Transformation of vesicular into cubic nanoparticles by autoclaving of aqueous monoolein/poloxamer dispersions.

The ultrastructure of aqueous colloidal dispersions of the cubic monoolein/poloxamer 407/water phase, in particular the particle size distribution and presence of an additional vesicular fraction, highly depends on composition and preparation parameters. Therefore, the effect of autoclaving on such dispersions was investigated. Before autoclaving at 121 degrees C, a dispersion of 4.6% monoolein/0.4% poloxamer predominantly consists of cubic particles beside a fraction of non-cubic particles. The small vesicular particles disappear almost completely upon autoclaving whereas larger particles with cubic structure remain in the sample. In contrast, a 4.4% monoolein/0.6% poloxamer dispersion contains predominantly small vesicular particles before heat treatment. After autoclaving, the majority of the particles is larger and of cubic structure and only a few small non-cubic particles remain. The effect can already be observed at short autoclaving times (e.g., 5 min) but a temperature of at least 90 degrees C is required to induce a major change in the ultrastructure. Results from temperature dependent small angle X-ray diffraction investigations indicate that temperatures corresponding to an isotropic phase are required for particle transformation. Heat treatment of monoolein/poloxamer dispersions can thus be used to transform vesicular dispersions into dispersions of cubic phase or to improve the cubic/non-cubic particle ratio in dispersions already containing particles with cubic internal structure.     

On the dilution behaviour of immuno-stimulating complexes (ISCOMs)

Immunostimulating complexes (ISCOMs) are used as potent vaccine delivery systems. However, the mechanisms by which ISCOMs work are mostly unknown. The immunological potency of ISCOMs has often been associated with their characteristic cage-like structure. Since ISCOMs can be regarded as composite mixed micelles that contain Quillaja saponin as the surfactant, we postulated a micelle to vesicle transition of the particles upon dilution with aqueous solutions. The dilution behaviour of ISCOMs is not only an important preparative aspect, but may also be of high relevance for both cell culture and in vivo applications in which dilutions occur. Crude and purified preparations of ISCOM matrices were prepared by dialysis. Methods used to analyse the micelle to vesicle transitions were transmission electron microscopy and dynamic light scattering. Significant morphological changes occurred upon dilution with TRIS buffered saline and non-buffered saline, and a step-wise transition from the typical cage-like structure via both less well defined ISCOM-like structures and helical micelles to small lipidic particles was observed. Aggregation of the resulting small lipidic particles was noted. The results obtained by dynamic light scattering complemented these findings. With increasing dilution factors, increase in particle size and polydispersity was observed. Zeta-potentials showed a trend towards less negative values upon dilution, indicating that saponins were not retained within the lipid matrix. The results indicated that at least partial separation of Quillaja saponins from the remaining colloidal species occurred upon dilution with aqueous solutions. The release of saponins upon dilution may be an important aspect of how ISCOMs work.     

Influence of preparation conditions and heat treatment on the properties of supercooled smectic cholesteryl myristate nanoparticles.

Colloidal dispersions of cholesterol esters in the supercooled smectic state are under investigation as a novel drug carrier system in particular with respect to parenteral application. In the present study, suitable conditions for the homogenization of cholesteryl myristate dispersions stabilized with a phospholipid/bile salt blend were evaluated. For effective particle size reduction homogenization with high pressure and at temperatures above the melting temperature of the cholesterol ester (isotropic melt) is necessary. Homogenization at lower temperature where the matrix lipid is in the smectic state is less effective even when applying the highest homogenization pressure possible but still leads to dispersions with particles in the colloidal size range. Since sterility is required for parenteral medications and is usually achieved by autoclaving for aqueous systems, the physical and chemical stability of cholesteryl myristate nanoparticles stabilized with different surface active agents during heat treatment was investigated as well. The dispersions were characterized by particle size and zeta potential measurements, differential scanning calorimetry (DSC) and high performance thin layer chromatography (HPTLC). The results indicate that cholesteryl myristate nanoparticles stabilized with phospholipid/sodium glycocholate, polyvinyl alcohol, poloxamer and poloxamine can be sterilized by autoclaving. Compared to cholesterol ester free dispersions of phospholipids, the phospholipid seems to be more stable against hydrolysis during prolonged heat treatment in the phospholipid/bile salt containing cholesteryl myristate dispersions.     

A comparative study of cationic liposome and niosome-based adjuvant systems for protein subunit vaccines: characterisation, environmental scanning electron microscopy and immunisation studies in mice

Vesicular adjuvant systems composing dimethyldioctadecylammonium (DDA) can promote both cell-mediated and humoral immune responses to the tuberculosis vaccine fusion protein in mice. However, these DDA preparations were found to be physically unstable, forming aggregates under ambient storage conditions. Therefore there is a need to improve the stability of such systems without undermining their potent adjuvanticity. To this end, the effect of incorporating non-ionic surfactants, such as 1-monopalmitoyl glycerol (MP), in addition to cholesterol (Chol) and trehalose 6,6'-dibehenate (TDB), on the stability and efficacy of these vaccine delivery systems was investigated. Differential scanning calorimetry revealed a reduction in the phase transition temperature (T(c)) of DDA-based vesicles by approximately 12 degrees C when MP and cholesterol (1:1 molar ratio) were incorporated into the DDA system. Transmission electron microscopy (TEM) revealed the addition of MP to DDA vesicles resulted in the formation of multi-lamellar vesicles. Environmental scanning electron microscopy (ESEM) of MP-Chol-DDA-TDB (16:16:4:0.5 micromol) indicated that incorporation of antigen led to increased stability of the vesicles, perhaps as a result of the antigen embedding within the vesicle bilayers. At 4 degrees C DDA liposomes showed significant vesicle aggregation after 28 days, although addition of MP-Chol or TDB was shown to inhibit this instability. Alternatively, at 25 degrees C only the MP-based systems retained their original size. The presence of MP within the vesicle formulation was also shown to promote a sustained release of antigen in-vitro. The adjuvant activity of various systems was tested in mice against three subunit antigens, including mycobacterial fusion protein Ag85B-ESAT-6, and two malarial antigens (Merozoite surface protein 1, MSP1, and the glutamate rich protein, GLURP). The MP- and DDA-based systems induced antibody responses at comparable levels whereas the DDA-based systems induced more powerful cell-mediated immune responses.     

Liposomal incorporation of Artemisia arborescens L. essential oil and in vitro antiviral activity.

The effect of liposomal inclusion on the in vitro antiherpetic activity of Artemisia arborescens L. essential oil was investigated. In order to study the influence of vesicle structure and composition on the antiviral activity of the vesicle-incorporated oil, multilamellar (MLV) and unilamellar (SUV) positively charged liposomes were prepared by the film method and sonication. Liposomes were obtained from hydrogenated (P90H) and non-hydrogenated (P90) soy phosphatidylcholine. Formulations were examined for their stability for over one year, monitoring the oil leakage from vesicles and the average size distribution. The antiviral activity was studied against Herpes simplex virus type 1 (HSV-1) by a quantitative tetrazolium-based colorimetric method. Results showed that Artemisia essential oil can be incorporated in good amounts in the prepared vesicular dispersions. Stability studies pointed out that vesicle dispersions were very stable for at least six months and neither oil leakage nor vesicle size alteration occurred during this period. After one year of storage oil retention was still good, but vesicle fusion was present. Antiviral assays demonstrated that the liposomal incorporation of A. arborescens essential oil enhanced its in vitro antiherpetic activity especially when vesicles were made with P90H. On the contrary, no significant difference in antiviral activity was observed between the free and SUV-incorporated oil.     

A new vesicle-loaded hydrogel system suitable for topical applications: preparation and characterization

PURPOSE. Aim of this research was to prepare and study drug release from a new formulation consisting of non ionic surfactant vesicular structures, niosomes (NSVs), loaded with model molecules calcein (CALC), nile red (NR), ibuprofen (IBU) or caffeine (CAFF), and embedded in a hydrogel matrix. METHODS. The system locust bean gum/xanthan (1:1), prepared at 60 °C, was used to entrap the vesicles (Tween 20/cholesterol 1:1), loaded with guest molecules and the release profiles were detected at 32 °C. The hydrogel systems were characterized by means of scanning electron microscopy; niosomes were characterized by means of size and ?-potential measurements. RESULTS. Size measurements showed that a slight increase in vesicle dimensions occurs after inclusion of CALC or CAFF (hydrophilic molecules) in the vesicular structures. ?-potential measurements showed that the inclusion of these molecules did not significantly modify the surface charge of empty vesicles. This was probably related to an almost negligible drug adsorption on the vesicle surface. The release from the niosomes-gel systems of two probes (CALC and NR) showed that the diffusion of CALC through the gel was not affected by the niosome entrapment while for NR, the presence of vesicles was crucial. The release profiles from niosomes-gel systems and from the hydrogel alone of model drugs, CAFF and IBU, showed an appreciable difference between the two drugs: the more hydrophilic CAFF was released much faster than IBU. In all release studies turbidity, dimension and ?-potential analyses indicated that the loaded niosomes were released by the hydrogel matrix without being damaged. CONCLUSIONS. The reported in vitro experiments show the capability of the novel formulation to combine the qualities of both chosen single systems, i.e. the niosomes and the polymeric network. The hydrogel shows a protective effect on vesicle integrity and leads to a slow release of the loaded model molecules from the polysaccharidic system. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.